I briefly explored MelonLoader but it was also coming up short. This was quite a while ago, but if I recall correctly, the most egregious issues stemmed from the fact that I was touching deep internal parts of Unity's render pipeline. One of the last issues to be fixed was some RenderTexture-related code not being unhollowed correctly.

Halfway through 2020 the switch to Il2CPP happened and around March 2021 I was messaging with Knah, getting the aforementioned issues fixed in Unhollower before the fixes even made their way to being used in either MelonLoader or BepInEx.

il2cppdumper definitely helps a lot but the devil is in the details. Getting something specific fixed might involve understanding the interplay of many classes and methods which means having to decompile all of them, tediously.