Good news/bad news. The bad news is, Apple is probably never going to tell us things like their algorithms for divvying up CPU core usage in Auto mode, or what the M-series performance cores are and are not capable of. This stuff is behind the curtain, and will probably stay that way. So trying to infer what they are doing with them, and (worse) what they will do in the future, is an exercise in futility.
The good news is that the folks who are responsible for the Logic code - and its algorithms for utilizing M-series CPU resources - are in a better position than the developers of any other DAW to make the best decisions on this topic. That's a big benefit of designing the CPU in-house. There are facets and features of the M series - and of the macOS multithreading support which uses it - that Apple may never tell anyone outside of Apple. But Apple developers - including the folks working on Logic - are privy to these secrets. We, the users of Logic, get a huge benefit from this. Logic may always have better utilization of M-series multithreading capability than any other DAW. Even if we, the lowly users, don't understand exactly why. 🙂
I'm all for experimenting, trying different configurations, measuring the performance of Auto multithreading, etc. I've done a fair amount myself. But I'd wager that Auto core management is going to yield the best performance in most (not all, but in the vast majority of) cases....because the folks who implement Logic multithreading know things about the hardware and OS that we will never know.