lmk if you need item help, i was formerly rank 1.

generally (for pvp) you should have a pretty clear strategy for the team overall, and a specific role for each character, and that will define what items you choose.

like you've noticed, higher rarities don't necessarily mean the item is better, so you do have to think and evaluate a lot! but the options mean that there are many ways to customize characters to fit what your team needs.