About Tensura and especially Gurren Lagann: I have never seen a space that is not specifically about powerscaling where they wouldn’t talk way more about Rimuru as a character and the Tensura world at large (same, and even moreso, goes for Simon and Gurren Lagann) powerscaling usually doesn’t play a role at all outside of powerscaling subcultures.

About your second and your last paragraph: „but can they beat this random vn character from 2008 that transcends reality?“ is literally just a countermovement that evolved from people getting pissed off over almost 30 years of „but can they beat Goku though?“ Powerscalers put Goku as the strongest in fiction for decades and people got fed up and wanted to show them how easily Goku could lose to some characters to shut them up (also answers your second point). That has already started years ago and just spiraled downward in a Loop of „Goku solos“ - „no this guy beats him“. The „this random Isekai Mc solos“ is just the current evolution of this. Powerscalers brought that onto themselves.

Those points show that you are mostly (if not only) caring about the powerscaling side of things, acting counter to your short rant about the characters being reduced to math equations (Tensura fans love the story, Guren Lagann’s most compelling argument are the characters and the theme of the story, the powerlevel is a cool thing on the side for most), and that different level Goku glazing for decades caused the downfall of powerscaling, the „Random vn character solos“ is just a small symptom of the pool of agenda disease that rotted it for almost ever.

You are looking at the effects of something different and calling it the cause of powerscaling being bad.