I can't say much because it's been a while since I played the game on a Pure run-my save file was lost so since then I just played on an easy difficulty and went corrupt. I wonder which difficulty you're playing with, just standard right? Personally I understand Aura making her companions look like meatshields in comparison- it's practically part of the story that they're weak as hell compared to her and pretty much hold her back. (But I see how you don't find it fun anyway.)
What helped me was planning my actions and upgrades ahead of time-and having a strong Slimie. But I think you're right in that the other companions probably just need to be more durable-maybe a lot more durable, but in return more AoE damage from bosses so you can't win due to bosses just attacking companions that block. If we can gift them books, maybe more books for them to increase HP, or gift components to upgrade their armour, etc.