Ok, I agree; Stealth can be useful but only if you use it at the right time. Personally I think stealth just gives me more time to figure out were my target is at, the best way to kill him, and if it is safe for my runner to come in with the flag. I played a few AA games today though and payed more attention to the random players that use stealth... well, lol, most of them don't do it right You'd have to me a more skilled player to pull off a stealthy move. My suggestion: be stealthy if your waiting for the enemy carrier on their side... that's really it.
Another thing is with good defenders. Good defenders won't head straight for your base. They will find the quickest way to cut you off and that does not include sitting at the enemy base (unless you're already that close). They will try to cut you off ASAP. Good defenders that know that the thief has no abilities won't wait or even give him the chance to get his abilities back.
Finally, the smoke-teleporter..... LMAO! It is sooo easy to counter that. I use knifes most of the time but also counter teleport. Really, counter teleporting is just as easy as throwing a knife, smoke bomb, using mute, or aerial killing them. It's not a big deal at all. All you have to do is watch their pattern and predict their teleporting spot :3 it's fun to teli-kill too. You guys should try it!
Again these are all just my opinions <3 All of you have really good points!