And what if you take out your disclaimer about more dense pixels? I.e. what if you're comparing a 24MP APS-C to a 61MP FF? Does the APS-C have an inherent advantage? I think it doesn't.
A7R IV is a bit of an anomaly, right now it's the highest resolution camera on the market, aside from Fuji's medium-format offerings. I imagine APS-C camera will catch up to ~50mp eventually. On the other hand, if you compare, say, A6600 with A7 III, the former will enjoy a DoF advantage. I've seen some macro shots taken with TG-6 that I simply cannot replicate with my A6300, like a leaf full of sheep nudis with everything in focus - I can barely get one of those into proper DoF, and full-frame is worse.