More of "If this was the only oil available, would you trust it in any motor you got, or are there potential applications where it would cause harm?"
It would, and it does. Reason why I felt like the shared sump category should be excluded is - all things being equal (ambient temp, mileage, OCI) the oil in a shared sump will be beat up badly in 5k OCI, compared to a separate sump with the same 5k OCI.
Good point. But if (for whatever imaginable reason) that was the only option available for long term, then I wonder how that would affect the intake runners and the cleaning interval? Intake ports and valves on a GDI need to be cleaned no matter what oil is used, but I never saw any info (school me if I missed it) on how using HDEO in GDI affects the carbon buildup and LSPI issues, vs using LSPI-battling oil. For example: are we talking 80k-100k intervals on recommended oils VS 60k-80k on HDEO between manual cleaning? or way more often? I just don't know, will research.
But that's what it is though - how much better are purpose built lubricants truly? If they are 100%-500% more expensive, does that proportionally reflect on their performance as well? Or are we as consumers paying 300% premium for 25% increase in performance? Just throwing numbers out there... But hope my point comes across.
I guess mainly what "grinds my gears" is - Could an HDEO 15W40 just be used long term across the board, with only adjustment being the length of the OCI? And if not - then which applications are a 100% NO-GO for the Super Tech 15W40 HDEO?