King of lightweight, FRM has in the past built the golden Ritchey WCS hubs. Obviously, being so lightweight, the stuff has, occasionally, durability issues, but not more than Tune or Middleburn. Thay made frames and components, and are still active.
I really love my 1x11. Lighter, more practical, nicer. Would never go back to 2x or 3x. Concerning flat bar gravel bikes, I've just tried this setup on my Merlin. I went back to drops after one ride, tho