While modding Minecraft 1.19.2 is pain, the pain mainly came from undocumented mojang's code, where you have to guess and validate your hypothesis before you write your code.

Modding Minecraft 1.8.9 is pain in the ass because of the barely working toolchains. Back then Minecraft's code is fairly easy to guess and work with. But the toolchain is unstable enough that literally several minutes ago it still launch Minecraft client properly. Then I close the game, made some change to the code, run the client again to test the change, and now it refuse to work. The runClient task finished successfully without launching the actual client and didn't give any error.

No matter how I cleared the cache, rebuild the project, it just refuses to work.