It made certain classes VERY powerful, such as the tech priest, who gets both science abilities and combat ones plus exclusive bionics, thus making dedicated warriors feel useless.
The other classes didn't have much choice regarding character advancement, yes.
You're still limited by xp though, but they were pretty good yeah. But scum and assassins could get stealth, guardsmen could get some talking abilities, techpriests got neither.
Although I'm certain most classes had mandatory stuff such as having weapon proficiencies, even if it was very late.
Iirc adepts didn't get a single ranged weapon proficiency until level 3 or something (and for all the talk of prestige classes, there weren't that many, any many had stringent rp requirements and were not that different from the base class). And at that point guardsmen had access to heavy weapons. You also had stuff like dual wielding, multiple melee attacks per turn, different stat costs (paying 800xp for a total of +20 is very different from paying 500xp for +5) which made classes feel differently good at stuff.
Could you purchase talents/skills outside your career for a premium price, the way fantasy did?
Iirc there was some "you can talk to your gm about making your own prestige class, or about buying a skill outside the regular advancement" but nothing concrete. I don't recall fantasy having concrete rules for it either?
