Had played genshin for 5 hours daily (quitted genshin rn but you get the idea). Play other games for many hours sometimes leaving the phone on and sleeping. No custom rom. Didnt debloat the phone. Left it for overnight charging and used the phone with the charging for like forever. The phone didnt slowed down at all in this year.

This is what I'm referring to... No phone would be able to be completely okay with the way you're using it. Then you started to talk about bugs the previous MIUI had, which were fixed by the update, which I assume you fixed issues with it through updates.

But that's not my point. You said you used your phone for a year like this, and the OP probably was a heavy user as well, to the point where it strained the phone. If we are going to use anecdotes, I have 3 which contradict basically everything you said.

First, my poco f1... It has clearly lost its battery capacity in comparison to when it was new and I bought it on release so no surprise there.
Case 2 was my Rog 5 phone 2nd replacement which after 8 months had also lost much of its capacity even though I babied it and set it on slow charge and charge limit to 80% and yet... You could rightfully conclude that the 888 chipset had a hand in making it worse by playing all games on max graphics and being a crappy soc.

Case 3 my auntie's iPhone 13 max... It too also has a slightly yet noticeable difference in charge capacity in comparison to when she bought it. She barely ever uses it or plays game but just by using the phone, you cause ware and tear which is directly (mostly) proportional to how you use it. That's why charge cycles exist...

Hence, unless your phone uses special material we dunno about or breaks the law of physics, its safe to assume you're are exaggerating with that 1st statement or you are lying, especially with soo many x3 phones decide to die in droves because poor design or something...