I think Tim had, at that time, the ability to bring out certain positive things in people. These things weren't necessarily in him, but he evoked them from his associates.
Maybe. I get the impression he was a really solid project lead with a clear vision (something he's seemingly not really managed to replicate in any subsequent project).
I've seen him give a talk on the history of the game and Fallout does seem to have been largely his creation. I'm sure most of what makes it so great came from elsewhere (Scott Campbell is, some say, the unsung hero) but Tim was the one who set out to make a GURPS-based cRPG, came up with the retrofuturism stuff, came up with the "three ways to solve any quest" concept, identified key sources of aesthetic inspiration like City of Lost Children, and ultimately was responsible for what did and didn't get approved for the game.
In one of his YT vids he was talking about how insanely hard it was to get people to do things at Obsidian while making TOW because everyone acted like babies (him writing people's names next to assignments on a whiteboard was seen as hostile or something, and people threatened to leave when he made a daily goal list), so from that I assume that he was doing a lot of effective organising and directing with Fallout.