You're taking the message completely wrongHere's the thing ...when your engines in good Nick and you drive well there is probably not much diff cause U are not making a lot of carbon and sludge
However I had a Hyundai accent with a fully sludged motor bottom and top and tried EVERYTHING on it from diesel to ATF to Kero to acetone to all the usual engine oil treatments
In between I was taking off the rocker and sump and photographing how much sludge was removed
Guess what worked !
Full synthetic oil .. followed by acetone(harsh not recommended) then ATP
dropped the sludge off the top and bottom
So FULL synthetic oil ABSOLUTELY WILL remove baked on sludge and carbon
Semi synthetic doesn't work not do any of the oil flush additives including liquid moly...what they do is just drop out the surface carbon...thats not necessarily a good thing as it may be helping your compression...they did nothing to the baked on burnt sludge all over the top and bottom of the engine
On expensive vs cheaper oils . I would say it depends on how hard you drive and how old the motor is..
The more important thing is how often U change the oil as even cheap oil has good protection for 5000km
I had to change the oil every 3 to 5000 km while desludging and the engine is over 215,000 kmh but runs like new despite being badly sludged and overheating for 100,000 km of that...so I think that the more often you change is probably more important than all the marketing around the oils