Edge can STILL work in the ring plus he has name value to bring eyeballs on the product. So you're getting BOTH from him. You don't bring him in just for some last hurray with Christian, you bring him in for the potential feuds with Starks, Omega, MJF, Cole, White, Hangman, etc.
injuries are apart of the business. Bryan Danielson had past injury problems too but NOW he's delivering the best work of his career. He literally had a 5 star classic with Zack Sabre Jr last night. If Danielson can do it Edge can do it.
Don't let Nostalgia hinder you from enjoying great wrestling. It shouldn't matter who's in what promotion as long as quality wrestling comes from it that's all that should matter.