Steal is nice to have, but nothing to center a build around, yes. Of course you can do that, but there are better ways to play a thief. Everyone has to find their own personal balance between “beeing usefull to the team” and “play how I want”.
Since I can’t know whats the most fun for you, I will focus only on the “beeing usefull” part. Thats a thing I didn’t like about the video linked here: It talks a lot about YOUR personal playstyle, but thats as usefull as someone saying: Do whatever you want, as long as you’re having fun.
Thats not wrong, but yeah, awesome, very usefull, that’s why I visit a forum.
Okay, on stealth: In PvE combat, stealth is useful for 1) dealing damage via Backstab and 2) for those “oh, sheeet I messed up” moments. But for general survivability and sustain its borderline useless. If you stealth yourself in a dungeon, the mob that just wanted to hit you now attacks another player. But you need to migate damage, not outsource it. And while you’re invisible, you are 100% useless. Well, you can rezz people, but beeing a walking rezzbot is still pretty bad^^. You only want to be invisible for the shortest possible duration.
So yeah, don’t dissapear. Dodge! And 15 points in acrobatics do help with that.
Another mechanic to migate damage is blind. Here is an easy step-by-step guide on: How to kill most non-elite mobs in this game:
Step one: Autoattack.
Step two: Use Blackpowder (pistol 5) every 5 seconds.
…
The end.
Now for backstab. In dungeons, you shoud focus on sustained damage. Not one big fat op backstab, but many slightly smaler backstabs EVERY 4 SECONDS. In shadow arts, you have acces to a trait, that restores 2 initiative everytime you enter stealth. Boom, here you go, endless backstabs. Use dagger/dagger BS for singel targets and sword/pistol with the already mentioned blind field for multiple weaker mobs. Or just use shortbow. Depends on your team.
