While googling I saw some references to the DT Swiss offset stems. Didn't seem like they were available any more (?)
My rims are Bontrager Duster Elites.
Yeah, agree with well-biked. The Muc-off nut is a little bit larger. An O-ring is included in the Muc-off valve stems. There's a recess inside the Muc-off valve nuts that covers the O-ring as you tighten the nut. Like many of you have mentioned, the sealing is done inside the rim, not outside, but I liked the idea of the O-ring anyway.
If nobody has a problem with the valve nut perching on one edge, then I guess I should just move on. I've got very little experience with t/l and it's entirely possible that the things that trouble me are non-issues.