Fultz doesn't appear to play a lot of defense, to me. Stylistically he looks most like Deangelo Russell. I guess I'm not sure I see the consensus #1 top pick others do. But I've only seen highlight reels, so I don't put too much stock in my own impression.
As for Lonzo Ball, I'm even less impressed by what I've seen. He has a weird jumpshot motion reminiscent of Kevin Martin (who was, to be fair, an excellent shooter). He's very upright generally. I'm not sure how good he is defensively. He doesn't appear like a super physical player.
I guess what I want in a potential top 3 pick is somebody with potentially game changing size or athleticism. E.g. Embiid, Porzingis, Towns, Wiggins, Giannis, etc.