Craigos, I think your projecting what worked for you onto Felix.
he from the sounds of it, rides harder and much faster than you or I ever did. And now you’re expecting your casserole of a drivetrain mix to last longer than a week. If it’s not working as per the manufacturer specs and installed correctly then that is grounds for warranty. If it’s all top end speed he’s chasing get him fitter and put/ keep a 34 on front.
Your hate for 12 speed I really don’t understand, it’s a proven on World Cup level racing across multiple disciplines as well as many happy punters (me included). I think you’ve probably spent more money and time with your experiments that just buying a 12 speed group set and being done with it.
If expense of parts is an issue put on a 12 speed deore until his riding improves to where he’s not constantly breaking shit. And with the money you’ve saved get him some lessons with pro, I believe you’re never too good to take on further advice.
It’s 2021 and bikes have honestly never been better.
Except Shimano brakes and the plastic master cylinders. FUCK YOU SHIMANO.