We've been over this hundreds of times it seems ...
What is required for compliance with Ford's warranty coverage is a lube that meets their spec; the Ford spec for lubricants (currently the F1).
What is "recommended" for a service factor is NOT the deciding factor regarding warranty, despite all the shenanigans to the contrary.
For anything that meets the Ford spec (dino or syn or semi), the burden of proof for any warranty claim denial would be upon Ford.
If Ford had a different spec for different grades, unique to each grade, and then required those via the service factor severity, I would agree with you. But they don't; the official spec (F1 level) does not delineate grades
; they are all approved under one license spec
. Hence, any lube meeting Ford's spec will assure warranty coverage.
If you used a licensed F1 spec'd 10w-30 and had an engine issue during "severe" use, the burden of a warranty denial would be upon Ford to show why your use of a licensed product was unacceptable to an arbiter, and then explain why the licensed product was not delineated by grade. Grade recommendations are only that; they are suggestions. Suggestions are not "licensed", and therefore not enforceable in court or arbitration.
Using this direct link:https://www.fcsdchemicalsandlubricants.com/main/product.asp?product=Diesel
Motor Oils Meeting Ford WSS-M2C171-F1&category=Motor Oil
Note that the previous link I had, to the F1 list, was dated 11-27-17, and that is the same one using this parent link to their site.
To the best of my knowledge, the F1 current release is dated 11-27-17 as of today (2-8-18).
In fact, unless Ford officially mailed you a formal statement, specific to your VIN as the current registered owner (it must be printed on the letter by name and VIN), your only obligation for your 2015 PSD for Warranty coverage would be to use a lube that met the "former" (E) rated spec level. Ford cannot legally require you to use an "updated" spec lube AFTER the sale, unless they send you a letter specifically changing the official warranty requirement, which is based upon the printed materials at the time of publication at sale, and get your agreement. If you're ever received a "recall" notice, you'll always see that both the registered owner's name, and VIN, are on those letters. For them to change a warranty requirement AFTER the time of sale, they would have to legally advise you of such, to your specific address and by specific VIN, and then actually offer you a choice of accepting the "new" warranty conditions, or allowing for a refund (prorated). Any time they would "extend" or "improve" a warranty after sale, your consent is not required. But if they alter or limit the warranty in a more restrictive manner, they must get your consent or offer an out (at prorated level). Multiple consumer case-law decisions have found this is the case. Just because you are aware of the F1 changes, you are not obligated to follow them, unless you were notified formally and subsequently agreed to them.
Because the "E" spec level is essentially akin to CJ-4, it's not a big deal to you. Or, using a lube meeting the F1 spec would be OK too. But the grade has NOTHING to do with the license spec of the former E level or current F1 level
and would be a moot topic in court or arbitration.