Ah but you can have the best of both worlds. Here is one example:
https://bobistheoilguy.com/forums/threads/2013-ford-f-150-5-0l-15k-oci-hpl-pcmo-5w-20.398483/#post-7329937
And I do believe user direct rejection is going an eye watering 30k+ OCI on 0w-16 in his Toyota.
I remember seeing the data sheet say that it is GL-4 and GL-5 compatible because they do not use sulphur compounds as the main extreme pressure additives. Perhaps someone can link that? For what its worth I am running it in all 4 diffs of my vehicles and its been fine.
If the metal quality and heat treat suck then it doesn't matter, no oil will save you as we have seen in plenty of modern vehicles. Back to what ripcord said, it isn't just the ZDDP as the AF additive, boron and molybdenum are also big players in the game now as well.
It doesn’t need to have sky-high zddp with the addition of moly and boron is what he is saying. They all work together. This MOAR ZINC deal needs to die already!
I personally don’t want stuck rings and nasty ring grooves so from that perspective no, all oils hitting a spec are not the same. We have seen it on this site where an engine running on “top tier” full synthetic starts shedding carbon gunk when exposed to HPL or Valvoline Restore and Protect.
You will be fine at 6k miles, that is by no means pushing it. Look at the recent 23,310 mile Subaru UOA, he is doing fine. I do 10k and my outback is fine, granted it’s the port injected 2.5. As others have said, run it to the factory OCI, do a UOA, adjust from there. That should give you plenty...
I’m inclined to say this is a Subaru thing. My reports always have higher silicon and like you, have tried different filters and checked the intake multiple times.