Battle Wizard has a multitude of problems when compared to Sienna’s other two very strong carreers.
In essence, BW is a gimmick. Her abilities are just that: gimmicky. Both Pyro and Unchained have abilities that just synergize very well with each other and more importantly: blend melee and ranged very well. We don’t need to talk about UC in this regard. Pyro’s passive crit bonus tremendously helps her melee abilities as well and her active ability is straight forward. Both Pyro and UC have access to abilities that either help reduce overcharge generated or vent it in a multitude of ways. UC is unaffected by overcharge slowdown and Pyro has access to abilities to counteract it somewhat (he has access to TWO abilities that boost her attack speed).
BW’s passive abilities do jack for her melee. Spell charge speed is unimportant for melee. Automatically venting overcharge does nothing in melee. And when she has high overcharge, her melee slows down.
BW’s overall shtick of having overcharge vented by itself is nice and all, but if overcharge hampers your melee, you’re not going to melee. She has not passive damage bonus in form of crits or otherwise apart from the +10% ranged damage bonus she shares with Pyro.
Her talents don’t synergize too well, they are pretty much just defining very limited aspects. 100% BCR is a gimmick, which is nice to have for a defensive style of play, but the game is so heavily focused on offensive play that it rarely comes into play. Also, I find it VERY weird that a concept that boils down to “stand around and hold M2” qualifies as a carreer concept. Her overall design is just designed towards being boring. Her active ability works reasonably well (if it works at all, that is), but it lacks ANY kind of profile. Compare it to other charging abilities. Kruber gets to knock down and has offensive and defensive options to choose from. Keri dashes and deals damage and also has offensive, defensive and utility options. Same with Zealot and Slayer.
BW has the option to leap forword more or leap forward more. The stagger is unreliable at times. The firetrail can be utilized reasonably well with enough creativity and awareness, but it is absolutely no contest when compared to both Sienna’s two other carreers and other charging abilities. The firetrail is only useful as a CC or horde clearing tool in very confined spaces, otherwise, the AI will circle around it. It deals laughable damage. The area covered is very small. The option that the flames linger longer is a joke.
It also doesn’t help that BW has trouble generating temp health, her main ressource to vent overcharge. She has access to the two arguably worst options: stagger and kill. Stagger is unreliable because the stagger actually has to occur (so enemies climbing etc. don’t generate much) and her melee arsenal isn’t suited for it. It works very well with flamesword and okay-ish with mace (on heavy sweaps) but stales when compared to on cleave and on crit/headshot/creadshot. She also has, as already mentioned, no other ways to get rid of overcharge. Pyro has the venting and temp health option and reasonable temp health generation from melee (both because of talents and her melee being overall better because of crits). UC can increase her overcharge bar, reduce overcharge generated, vent by blocking or improve venting, he ability always vents. UC has an engaging playstyle that actively encourages you to switch between ranged and melee, literally playing with fire how risky you can be. For Pyro melee is definitely a secondary option, but she can handle herself due to SS essentially being up anytime she swings. He active ability can thin out hordes, too, and she ALSO has access to BCR ability tied to her already powerful crit chance increase.
Pyro and UC have a very distinct profile and are fun to play, I love their melee/ranged blend (especially since wigglemancer and ranged temp-health isn’t a thing anymore 
). BW is essentially Pyro without the crits and without the ability. Faster spellcharging is nice, but it doesn’t get you very far if your overcharge is so limited. 20% overcharge reduction is pretty much a must on staffs for her and even then, on staffs like bolt, you can’t do very much before your overcharge meter is red hot.
Speaking of staffs, people keep mentioning Conflag staff as being her staple. I agree, Conflag with spell-charge speed maxed is alot of fun - but is that REALLY all there is to BW? Conflag is already a rather situational weapon, requires alot of positioning and can even be annoying since it can spread hordes out due to the lingering flame (which enemies tend to maneuvre around) and tossing smaller enemies around instead of funneling. But at least Conflag is a staff where you can safeley say it is performing distinctively better on BW than on the other two carreers, since it’s overall nature doesn’t benefit from crits too well (making it less interesting for Pyro) and the slow charge speed makes it a little clumsy to use for both Pyro and UC (and as UC, you are better of going into melee due to the staff’s rather limited ranged on charged spells).
But the other staffs? They either perform either better on the other two or without much difference.
Fireball works at least as good on Pyro and UC because they have better overcharge management and Fireball’s strength doesn’t necessarily lie in the charged balls, but spamming uncharged balls - and here, overcharge is king. Put barrage on it (or in Pyro’s case, Hunter is a veritable option) and you are all set. Faster charged fireballs are nice, but that doesn’t synergize well with Barrage (or Hunter, for that matter) - and don’t forget that both these traits also boost melee damage!
Boltstaff works reasonably well, but again, it’s arguably better at least on Pyro because she can handle overcharge better. Both Pyro and BW can kit their Bolt to two-shot CW with headshots (which is very might, no question!), but Bolt being a rather mediocre staff in other regards (no zoom on a sniper staff, VERY high overcharge and absolutely ABYSMALLY low boss damage) still makes it at least even between Pyro and BW - and Pyro still has better crits (for more damage, especially against bosses) and can fire it more often before venting (when kitted right at least). The 10% less damage do mean that UC cannot hit the 2-headshot-breakpoint on CW without the help from other abilities (WHC tag is enough and since UC can sustain large amounts of overcharge, running Barrage or Hunter on it and then spamming light attacks on CW before charging up the bolts works wonders). The faster charging does mean you get those bolts out a little faster on BW but bolt generates such large amounts of heat that this advantage is very limited, and even with the 40% faster charging, you get 2 bolts out before the difference becomes hardly noticable again. Also, the charged bolt is usually used for targets at medium to medium-far ranges where charge speed isn’t all that important and BW’s advantage starts to melt (quite literally 
)
Flamethrower is more or less on an even playing field. It is a very overcharge-efficient staff, especially with the faster charging abilities from BW (with maxed out, you charge for maybe a second or two and can blast away at full charge), but imho, when push comes to shove, it is still better on Pyro and UC can also get more mileage out of it. Pyro can run Hunter on it for longer buff, which gives her a solide edge in melee, especially against armoured (stagger them in place and weaken them with your flames, then switch to melee and benefit from the 25% power vs. boost) and more importantly, her active ability can counter the staff’s biggest weakness: no long range. Even without CDR-trait, holding your flamethrower into a horde considerably charges your ability (even more so because she crits more often), so you have that burning head ready to deal with otherwise out of reach target. Pyro can also deal serious damage against CW with this staff, especially when on high overcharge due to crits piercing. UC can boost her already impressive melee damage even further with barrage, which again plays into an already existing synergy rather than creating it.
And don’t get me started on Beam. BW has nothing that gives her incentive to choose beam other than MAYBE burn-damage ticks - but since they are limited to one tick (and beam’s main boss killing power comes from the insane stacks of burning ticks), Beam is completely pointless on BW.
BW needs profile. BW needs something disctinctive. The infinite burning ticks I found to be an amazing idea, but BW needs to provide a foundation for something like this.
IMHO, BW should be about two things: damage over time and charged spells, both of which is are hinted at, but not executed till the end.
My suggestions after this WoT would be to explore these two aspects of BW.
Give BW a passive 50% bonus for all damage over time and make the infinite DoT talent increase that by an additional 25% or so. Make it so that her passive 10% damage buff is not for ranged damage, but for FLAME damage so it incorporates all of her melee attacks that deal fire damage. Give her the passive ability that all charged spells cost 20% less to cast and an option to increase that by another 15% or so.
Give her access to a DR-Talent on high overcharge (instead of DR while being disabled). How about an ability that generates temp health whenever an enemy dies from DoT?
BW could also be a prime candidate for being a 125 base health carreer. And by Aqshy, give her access to with temp health on cleave. BW is more or less designed as a CC and horde clearing carreer.
