It's not a plot hole. When Neva uses his magic, he brings back Goku's tail. The tail was always essential to the Great Ape and SSJ4 forms. I'm very sure by the end of Daima, Goku will lose his tail again and be unable to attain that level.

The red hair though I agree makes sense in that SSG is the closest you get to SSJ4 without a tail. This makes SSB essentially equivalent to SSJ5 which we all kinda felt it was anyway.