There’s a few different types of complaints about BB. Yes, some of it comes from ppl who can’t prioritize targets, can’t pre-charge with secondary, don’t even know how to slide around while charging. And yes, that’s a skill issue no doubt about it.
But some of it comes from a different place, from comparing BB to staves & the other blitzes.
Smite can stop every enemy dead in a huge area, cleaving through all oggies and reaching all disablers anywhere in there. It’s the equivalent of an actual ultimate ability, offering a total reversal & turning a certain wipe into a joke of a shooting gallery. All with with no CD, low peril cost, and once properly specced doing enough dmg to kill everything except oggies & muties in there while it does.
Assail lets you turn a group of gunners & ragers & most anything else into mush in the blink of an eye with barely any aiming required, can easily be mixed in with melee, and works as a long-range auto-aim sniper too. All with a very low CD. Both Smite & Assail are universally useful almost all the time, routinely making a big difference every time they’re used.
But BB? BB is a slow & expensive single target tool in a game where the threat is always in numbers. Even on single targets most staves do a better job, but there’s almost always more than 1 target so staves getting ahead isn’t really even a question. Ofc it can be useful and is if you know what you’re doing, but those uses are rare, and almost never make the kind of difference smite or assail would be doing. It’s more of a highly specialized support tool for the few builds with no other ranged & anti-armor options.
Sure you can turn it into a decent boss-killer with stuff like investing in Kinetic Resonance, Empyric Shock and Empowered Psionics with other buffs. But that’s a crazy amount of talent points & a keystone invested all to conditionally do about as much dmg as you could with a single bleed knife in literally any build at all. And even for all that investment, it’s unlikely for that BB to ever have the same impact a literal zero-invested smite can on a regular basis.
tldr; The problem is not that BB isn’t useful at all. It’s that the other blitzes enjoy a much higher frequency of being useful, with a lot less conditions, need a lot less skill to use, and overall have a much larger impact when you do use them.
I don’t even think it’s a serious problem myself. Not all weapons, abilities and classes are supposed to be exactly equal after all, that would just make for a boring game with no interesting choices. But it’s not hard to see why not all people are comfortable with that.