I think it's pretty certain that under Chevron and w/o W. Virginia vs. EPA the EPA could ban ICEs tomorrow and the courts would allow it, and Congress would be unable to stop it, but that would be a very drastic thing to do and it should require debate, and we wouldn't get it. If you don't think that scenario is likely, there are others somewhat less extreme and more likely ones one could conjure up.

I think that's abdication.

I don't think so. People have been complaining about Congress' dysfunction for decades, even when it was fully in the hands of one or the other party. I don't think Congress' dysfunction has anything to do with partisanship. And yes, "populists" get to have a voice -- that's what it means to have a representative democracy and republic. If "populists" (or whatever) need to be negotiated with, so be it, but it's not intransigence that makes Congress dysfunctional. I suspect the problem here is that you want activist agencies to ratchet-like interpret power delegations ever more broadly as long as you agree with those interpretations, but that is a very risky game.