I personally think UC is in a good spot. Some minor tweaks could however be beneficial.
My go-to weapons are flail + beam. With repeated use of the flail’s first heavy attack, UC can perma-stagger groups of everything (except CW). Very useful when holed up somewhere, or when playing Vanguard or Twins.
With Beam Staff, is really easy to raise overcharge with the shotgun blast. The beam itself is accurate even when actively taking damage, and is great at taking care of flamers and gunners targeting you.
Through careful overcharge management, UC can be almost indestructible, while at the same time be able to dish out decent damage. As long as you don’t blow up, UC can easily go through an entire mission without using a single healing item, thanks to DMG reduction and THP. When the overcharge bar is full because you got hit, you can push, dodge once and vent at the same time and then continue fighting.
Getting overcharge from being hit is an interesting aspect of UC, that adds to her uniqueness. If we were to remove this, we would have to reduce her damage reduction and change a lot of other things about her. Being able to raise overcharge by getting hit can also be useful, like when using certain ranged weapons that are slow at raising overcharge, or when you don’t have time to bring out your ranged weapon. Her damage reduction and THP on hit makes it easy to recover from such hits.
The ultimate being a panic button is a bit annoying, as it means I’ll save my ultimate until an emergency. Sometimes there are no emergencies, and suddenly I am at the end of the map, having not used the ult even once. But as long as it can save me from being downed if I mess up, then I’ll keep using it sparingly. What they could do is change Burning Dregs a bit and add it as a Passive instead of a Talent. Something similar to Zealot’s Heart of Iron. That would free up the ultimate a bit.
Unlike Pyro and BW, UC supports a more reckless playing style because of her tankiness. She handles chip damage very well, can out-vent gunner-fire and gas, and has her panic button. One thing I would like removed is overcharge from FF. Especially from bombs. Looking at you @James, you RV-player.
When it comes to talents, UC has several that could use some change.
Chain Reaction gives some extra, unreliable CC, at the cost of ATK speed or push+ignite. It is clearly not worth it.
Numb to Pain gives 5-15% extra DMG reduction, but only a short while after venting. Considering how damage reduction is calculated for UC, it is pretty useless. You could instead choose Conduit, which increases your survivability by a lot.
Dissipate seems counter-intuitive to me, as a UC should be staying at high overcharge. Dissipate actively makes this more difficult. It might increase survivability by a lot, but the cost to your DPS is too great.
Burning Dregs can be an additional safety net, but I find that it is unreliable and not needed because you have your ultimate. Since it activates depending on your HP and not your overcharge, it is often more damaging than helpful. Not only did you take a hit that sent you below 50% HP, you also lost all your Unstable Strength stacks.
Flame Wave is just inferior to the alternatives. You apply dot and weak stagger to a few more enemies, instead of healing your party or getting more stagger and DMG from your ult.
One last thing. CWs always gets past the overcharge’s safety net with their underhand swing when they hit you. It makes CWs much more dangerous to UC compared to any other class. Fixing this would make a big difference for UC.