Flash degradation literally only affects writes. Android has had TRIM since 2013. Writes in no universe make the OS run "noticeably slower" (or lead to "lag"), even if your claim was proven.

There are literally billions of Android devices. Benchmarking file system performance is trivial. Ergo, where are the benchmarks supporting your broad claims? This should be incredibly easy to demonstrate. We do know that it happened pre TRIM because people had factory new and after use benchmarks, and could show the decline.