STIHL oil is high quality--and likely overpriced, but since I run mostly STIHL stuff....
Well, anything non-STIHL gets Mystik, STIHL sure is expensive...
Husqvarna is also almost exclusively Chinese since 2 or 3 years ago...they put out a press release saying they built a plant in China and most of their manufacturing there, and recent quality suffered greatly for it I'm told by Husky owners. Maybe that's just a testament to how good they previously were (I think ECHO took Husky's #2 spot). Still, performance wise Husky beats STIHL, longevity wise the other way around, comfort wise it's Husky, design is STIHL, parts is Hysky (ECHO beats them both), etc...
I run the STIHL Kombi head at way less than max most of the time, it being a KM-131-R flat-out would be wayyyy too much, and though I run 50:1, like you I'm fine. The dealer did recently pull the screen out when I entered a pole saw competition, it's a bit louder/faster but there was no previous issue with carbon...then again I run heavy line flat-out when cutting wooded areas.
And like you I idle my saws (though they're tweaked and should be cooled down between cuts) and run non-ethanol high-octane gas (again, they're tweaked) and no issues. I really think it depends on the particular engine, but a lot of people hate STIHL oil, so they must have something "not quite right" or "not quite figured out," maybe. Since I run rich in non-STIHL saws I run Mystik, so maybe that's why I'm not seeing issues, but Mystik will run rich, STIHL oil not so much...