Erik,
I think you are "spot on".
Someone in my audio club who knows more about the "nuts and bolts" of DAC design than I'll ever know once said that the reason why hi-res files sounded better several years ago was that the DACs of the day had "quantization errors" and by processing a hi-res file, those errors were typically way beyond the upper limit of our hearing, so filtering them on the back end didn't have much of a negative side effect. He said that today's DACs have pretty much "solved" the "quantization error" problem.
I must say that, when I'm streaming music (from Qobuz), I usually select the hi-res file, not because it's hi-res, but I do suspect that they are newer masters and sometimes do sound more "musical" compared to the 44.1/16 files, but not always.
Your point is well taken, that the newer generation of DACs are so much better than one's from several years ago, that "regular" CD quality does successfully rival the sound quality of those hi-res files.