Yikes. It's getting increasingly difficult to find any vehicle that does not have a serious achilles heel or two, regardless of brand. I considered a Forester back in 2013 but the oil consumption internet frenzy scared me away. I don't look forward to my next purchase. Thank you for sharing your experience.
I clearly get your point. When Ford's incredible modular 4.6L was regularly making 500K miles without issue, all of a sudden the 5.4L version was suffering failure after failure. Many issues were due to design changes. But others were clearly "related" (not due to, as there is a difference) to the change to thinner oil and an increase in oil temps. The 5.4's suffered timing chain guide failures, due to leaking timing chain tensioners + low oil pressure due to the oil pump backplate leaking. Also head/cam failure as oil would not make it to the rear of the RH head. The problem is mechanical in nature, made visible by water thin oil.
HOWEVER, with a higher viscosity oil, those mechanical problems (small leaks) were not catastropic. The 5.4L "1.3 million mile van" used 10W-40 oil. That very same engine might suffer failure before 100K with 5W-20 here in FL.
I'm currently at 170,000 miles on my 5.4L, it gets a steady diet of M1, 10W-40HM and is running perfectly. I don't expect any issues. Contrast that with the guy who, at under 60,000 miles, changed his RH cylinder head and cam phasers due to low oil pressure, with the use of 5W-20 here in hot n sticky South Florida.
My point is not that "thin oil is bad", clearly it's not. But that certain engines do have known issues that can be addressed by a savvy owner. Choose a quality synthetic that retains adequate viscosity, and change it frequently.