Concerning ATF+4, which IMO was one of the 1st 'real' capable ATFs from an automaker, the spec is over a decade old. Have there been any changes to basestock's, VII's, additive technology........... in the past decade? Does anyone not see any room for improvement anywhere? Still waiting on ATF+5.
Concerning ANY boutique fluid from any boutique supplier, they've been improving on the factory spec's since they started their business. Automakers newer requirements, IMO, are simply trying to catch up with the boutique manufacturers. BTW, its also easier to spec a tougher fluid then to re-engineer a component to last longer. Usually, a new OE fluid is the automakers bandaid for an existing problem.
Lets say that 10 years ago I came out with the DexronVI formula and called it superduper-ATF. It wasn't licensed and didn't meet the DexIII specs, so many would argue against it. But, when the automaker does it, its ok.
Waiting for the automaker for an improvement is no different then being an ostrich with your head stuck in the sand. I wonder what Dexron-7 or 8 holds for us in the future.
Walmart is simply a reseller. With their volume, and their buying habits, they can claim anything they want. Also, the company is big enough to almost defeat anyone that challenges it. And, when you cut the price down, something has to suffer somewhere. Batch quality? test sample rate?
Concerning the Subaru, I'd go thicker. My votes for ATD.
If you're running high temps, consider a bigger cooler or sump.