Oblivion thieving isn't so difficult, and at least you can develop your skills by doing more thieving. You may have to pay the price of failure from time to time, but you never have to rely on combat experience to develop your thieving skills. And you can ghost the entire questline, with the exception of two vampires, you can pass without trace, witnessed by none, the only clue that you were there is the things that are missing. This is the ideal thief. Can't do that in Arcanum; the Thieves' Underground isn't too accomodating to developing thieves, and don't give jobs that match your skills. If you distribute your points evenly, you may be unable to do any job, and if you specialize in one skill, you may be stuck with a backlog of jobs requiring a different skill (and why the fuck do so many people NOT have keys to their own damn locks?!?) When you're left without thiefly ways to advance from a thiefly foundational skillset, all you can really do is order your followers to attack and watch them get their asses kicked, because they can't level up either. You'll level up more smoothly if you focus combat skills first, but that's really not a thiefly approach; you just aren't allowed one. What you do get is a redundant expenditure on two skills that should be one, traps, and another one that shows complete ignorance of actual combat, backstab. What bullshit.