yes sir. Right.
But coming back to my above example of gli n premeo, am sure we can feed 0/40, 0/30, 5/40 oil to it (without knowing what comes in manual because most jdms are without manual). But to the gli, we cannot feed fully synthetic oils (like premeo). Instead we will feed it 10/30 (as company recommends), 10/40, 15/40, or lets say 5/30.
But there will be sky high gap between the engine's working in both of these cars.
Premeo will give average like 11-13km/l but
gli will be steps behind.
Change intervals of premeo will be longer, whereas it will be pretty shorters for gli.
Etc. Etc.
At the bottom, it will be easier & cheaper to keep premeo as compare to gli.
Only we have to feed the right choice of oils to premeo and they dont even need very regular tuning. While for gli it will be necessary to have it checked after 4-5k for sure.