All great points. Subaru still does have the same owner's manual language that a thicker viscosity is required in high temps, although they do not define the high temps nor the thicker viscosity. But there's not much uoa data out there on this new engine. You can find maybe 2 or 3 uoa's. Someone on the Outback forum did post a 0W-20 uoa from a new XT that dropped to a 16 grade but I think that's to be expected.
The FA24DIT in the Ascent and new Outback/Legacy is supposed to be a more robust engine than the FA20DIT and Prime Motoring in NJ dropped an Ascent engine into a Crosstrek and is making 500+ whp on the stock block. The FA24 has thicker cylinder walls, more cylinder support molded into the casting, thicker rods, and stronger beehive valve springs (see video below). Can these components alone accommodate a lower grade oil? Not sure if bearing clearances have changed.
Back to the OP's question (or statement?). I don't think I'd be running a high SAPS oil in a Subaru DIT. If I used a high HTHS 5W-30, it would be Rotella T6 5W-30 MV, or an ACEA C3 oil, since those add packs would be a bit friendlier in regards to IVD and possible LSPI. There are lots of uoa's on the FA20DIT on nasioc where Resource Conserving 5W-30 showed low uoa wear metals using an oil with the operating viscosity of a 20 grade due to sheared and/or fuel diluted oil. Yes, there are a few posts about dealer serviced WRX's that had engine failure, but not at the level of the EJ's.
IAG Performance actually recommends reduced SAPS Motul X-clean in their built FA20DIT's. They only recommend Motul X-cess in their built EJ's.
Here's a video with some details of the FA24 where they also mention the Prime Motoring swapped Crosstrek.
Some quotes from Prime Motoring posted on nasioc (I think from PM's social media):
[Subaru] used the FA20 as a building block to learn and grow. Every weak or inefficient point on the FA20 has been improved upon.
The rods are still J shaped but way beefier
From what I can see so far, the future STI will be a great one. I was already a fan of the 2.0 but Subaru really improved on the weak areas. Also using FA24 cylinder heads and modifying them to work in an FA20 application. Only aftermarket part used was a set of ARP studs, everything else was new directly from Subaru. Goal of this is through trial and error, advance the FA platform further and give additional options to future customers. We will take it where no FA24 has been before and probably end up in many little pieces but this is the sacrifice we make for the future of Subaru performance