Hotsaws 101 is full of it!! This has all been beaten to death a million times, all angles have been looked at and discussed, we all have a good understanding of what's what, you're not providing any unknown information. Oil does more than just lubricate! Ultra is bottom of the barrel, burns very dirty at any ratio, It lubes OK though. The fact you have carbon issues should answer the question, the answer is right in front of you. Who ever told you 40:1 will make less power is in the business of selling new saws, not making them last or make more power. Pretty much everyone here recommends 40:1 or 32:1 so I don't know what you mean buy learning to run 50:1 from this site.A specialized hydrometer can easily check oil to fuel ratio. It literally takes minutes. A friend who raced a Honda CR125 professionally had one. Fairly inexpensive. But, yes, most dealers and techs don't have one. However, my 261 had a rattling noise and was sent to Virginia for a week before they sent it back. I'm sure they have the capability to test.
Carbon buildup had in fact cracked my piston. I set the squish to .019 in '09. In 2019, with the buildup the squish was .007! So yes, carbon cracked my piston. After I cleaned it the squish was .019.
Stihl oil is actually not bad at all. Hotsaws101 has a YouTube video all about mix oil and ratios. He's talked to manufacturers and specialists that helped him compare different qualities, viscosities, additives and select properties of multiple manufacturers. Stihl HP Ultra was hight on the quality list, and he even mentions the specifics of why it actually cleans carbon when mixed at 50:1.
In the post I linked, it is explained, by multiple people here, that oil molecules are larger than gasoline molecules, so more oil= less gas. Something that is easily tuned for by hand, but a system measuring volume cannot differentiate... Which is why you can still straight gas an MTronic.
It's also mentioned that oil doesn't cool anything, it is simply a lubricant. The gas actually has cooling properties (though barely significant). So if there's less cooling gasoline.... Yeah.... On a system that already has heat issues.
I wholeheartedly agree that manufacturers will weasel out of as much as they can.
If you start looking for an new car and want to know how good the engine is you ask an independent mechanic you trust, and do as much research as you can. What you're doing asking the salesman, you're listening to the salesmen, instead the mechanics and in some ceases engineers. They want you to believe they know all, when all they want is you to buy overpriced oil and a new tool as soon as possible. Some love Kool-Aid.