I've reached 27 on my assassin and by this point I would say the class can be heavily customised by gear, perks and skills. Also, plus stat on gear can change a lot on weapon abilities (e.g. -30% cooldown or +30%dmg on a weapon ability) so I don't feel boxed at all. Maybe Psykers can be customised even more, but that in itself might not be a problem.

Psyker gives you the illusion of customice options. A lot of skills are not worth it, there is only one weapon combo that is worth it. If you watch it from a effectivness point of view there are only 2-3 viable psyker skills. You have a lot of options that are simply not needed.

On the other side it's the most broken and OP class because the mechanics do not work right or Neocore overdid it... 100% crit anyone? 0 heat build or max heat build without consequenses. Best mobility ingame as tanky as a crusader if you want to. Do 600+ PR missions at level 6... yeah sounds legit.

That is, as a main weapon set, having at least in some builds the option to have most of the other weapon setups as a useful 2nd option for certain situations.

And on top of that, there are several different play styles, too.

And there are many useful skills, though many of them are a necessity, which is bad for the diversity of setups, but still,
I'd say less than half of the spells are useless in a way that they are seriously underpowered or not needed at all,
this leaves plenty of nice stuff to play with.

And given the OP-ness of psyker...
starting out on a fresh account, it is mediocre,
after getting a good bunch of the medium-grindiness-level things, it start's pulling ahead a good bit, being OP for that time,
after getting a certain super-grindy thing though, the others are no less viable to be super OP

I'd say it's ok-ish in terms of class balancing so far,
only the grind needed for several things is ... a "bit" off.