Hmm, it is interesting that [@NarcissisticPotato] decided to use Crowfall as an example. I don't think it necessarily a good choice of games because if I remember right the way a skill is increased is done passively but you set them up in a queue sort of like EvE Online. Plus the way classes are handed are fundamentally different than I imagine how Pariah would, but that also isn't exactly relevant at the moment either so I won't go any further into it, my point it Crowfall I found to be a weird comparison to use. Although I guess a lot could have changed by now, it has been a while since I last looked at the game's development. 

Anyway I would say a system like this would be more comparable to say... uh, well an elder scrolls game is what comes to mind so I'll go with Elder Scrolls Online. Where you increase skills through constant use, [i]now[/i] ESO is a poorer example since you still deal with traditional levels and traditional EXP bars, still it was the way that skills are improved is what I'm looking at. 

Also on the subject on achievements I don't have an issue with them, the way I say they should work is progress in a logical way that compliments normal development. So the achievements you get for just practicing a skill, like say "kill 100 monsters with a sword" eventually every swordsman will achieve this, but perhaps not this specific one. Another game I can point to is would be Civilization 6, weirdly enough, with the eureka system. You get a research boost for completing tasks that you would probably do anyway, just replace the research boost with another reward and those eurekas with achievements. Then totally there could be real difficult achievements out there, stuff that takes real work and danger to achieve. The bottom line though is while I completely believe Pariah should be built like a MMO, I don't know how in depth in achievements that would be practical for a roleplay.

Edit: Oh wait you did mention how Crowfall has the passive training... opps. My bad.