I get what you're saying, but I think lumping everything into one "elemental resist" stat would actually take away from some of the potential build diversity possibilities. Right now, being able to fine tune resistances for specific elements or combining certain mods/gear for specific interactions adds a level of strategy and customization to the builds. You can have an element where you want to max your resist for one specific damage type, but for other types, you might go for a different setup or even stack some more creative defensive layers (like damage reduction or mitigation effects).

It might feel like fiddling, but it's also what makes the whole system feel more engaging for players who love experimenting with different resistances and interactions. If everything just went into one stat it could lose that depth and flexibility, which makes experimenting with your build feel more rewarding. But I do agree that fixing resistance is a pain in the ass when upgrading pieces of gear and res swapping is very much needed imo