Better read the Briggs oil recommendations more carefully.
5W-30 full syn is best in cooler operating temps
to as high as 120° F (-30 to 40° C) providing the best protection at all temperatures as well as improved starting with less oil consumption. For temps above 80F Briggs says a 15w-50 full offers the best protection.
I would say the latter conditions are where the majority of mowers and lawn tractors see the most action. If fact Briggs states-:
For continuous-use, such as commercial lawn cutting or pressure washing, use Vanguard 15W-50 Oil (temperatures from 20°F to 130°F).
https://www.briggsandstratton.com/na/en_...ChoosingOilType
I added the rest about 5W-30 full syn that you left out and I'm not mowing grass all day long so I don't fall in the continous use / commercial cutting category.
The way I read it, Briggs claims 5w-30 full syn offers the best protection over the broadest temp range with improved starting (i.e. in cold temps) with
less oil consumption, implying there may be oil consumption, just less so.
Interestingly, for the most punishing conditions above 20F (commercial and continuos use- pressure washers, generators) Briggs suggests 15w-50 full syn. Therefore, that would seem to be best OPE oil if a choice were made.
Why they exclude HDEO oils altogether I don't understand.
Actually, anything you don't normally run in the winter would make 15w50 look like the better choice. Think about it, its still thinner at start up than the old stalwart recommendation SAE 30.
