Fury 3 struggle

No, that sounds like a waste of pure potential. +Atk/-Res Eldigan can be used, even if it's only for Arena Assault.

Eldigan is a great unit with a fantastic refine, and your IV statspread on him is almost perfect. I'd say that you should definitely hang on to him and try to fit him into a cavalry team. If you're short on Hinata, you could use Jagen or Bartre and just inherit Fury 2 on units who need it, or use substitutes. Or, if you did the Fallen Takumi GHB, you can use him for fodder.

+Atk -Res is arguably optimal. Eldigan can become very powerful with his new refine. The ability to run one of the best A slots in the game alongside a second one is very powerful.