Moving stack size changes to data_final_fixes has broken support in my mod for adapting to your changes. I need to dynamically adjust recipes based on what the stack size for a range of items is. If you put it in data_final_fixes, there's no way for other people to reliably catch your changes.

You can always catch my changes by adding ReStack as (optional) dependency.

Should I be searching for every other mod that changes vanilla stack sizes as well?

If you want your mod to be compatible with any mod out there you have two options.
1) Get every other mod author to use final-fixes as read only. Never going to happen, I tried. That's why i swapped back to final-fixes.
2) Add popular mods as optional dependency and other incompatible mods as they pop up.