Yeyasher Kochacha! That was a very thorough exposition on were the zohar stands in the rules of psak. It even explains why there are stiros between how RiSHBi paskens in the gemara and what he says in Zohar. Just a couple of points you raised:
1- You mention toras kohanim. I didn’t use it as an example, but it actually is the best example of what I’m talking about. THe midrashei halacha were written by tannaim and were very meduyak (even more than the baraisos of Rabi Oshiya) hence we pasken like them far more than the medrashei aggadda which are less meduyak, as you point out, and are not always even meant to be din.
2- You write: Those who relate more to Sohd will follow Sohd as much as possible. This is where the Teffilin on Chol Hamoed comes in. If not for the Zohar Hakadosh, the usual rules of Paskening would have everyone donning Teffilin on Chol Hamoed.
There is also the matter of family minhag. My father is less “sohd oriented” as you put it, yet he still wears tfillin on chol hamoed as do I, because that’s how he was taught and I do because it’s his minhag. So in a way, even by the normal rules of psak, people end up following sohd.
3-Although all Torah Lishma is real of course, the other explanations are like offshoots of the main trunk, while the Sohd is the trunk
Lav davka. Many acharonim paskened wihtout sohd because they held differently, but I see what you are saying.