The main problem is that Touch Bar is
essentially a bunch of toolbar items in most apps, and toolbars are probably more convenient. The more elaborate slider-like stuff is pretty rare and still not obviously better. Same for color picker; it's
limited compared to on-screen and less precise (so why use it?).
I would have loved an iPhone-shaped iOS environment that could run much more interesting things but perhaps have ways to integrate with the frontmost app (unlike a phone).