Actually, having thought about it, the issue - at least what I am experiencing - is not at all related to this.
I have stutter in all games that have ProMotion support, and whenever that is enabled, games stutter randomly after touch input. Without touch input it works perfectly. The same games also run flawless when ProMotion is turned off in the game (not system-side). I strongly suspect Apple has messed something up deep in the code, and even they are having a hard time figuring it out, if they're at all working on this with priority. I guess there aren't enough complaints coming in..