I've seen the same results with lower viscosity for PP, PUP, and Idemitsu Zepro Touring 5W-30, they all seem to be closer to 5W-20 after 4-6k of use.
Exactly. Brand doesn’t matter. Look through this entire thread and I think it would be difficult to come up with more than a few uoa’s of a GF5 5W30 that stayed in grade, even at 3k miles or less.
It’s normal for turbocharged Subaru’s and, with a Blackstone uoa, you can’t tell if the oil is shearing or if it’s fuel dilution since BS doesn’t actually test for it. They only estimate it based on an extrapolation of the flashpoint reading.