Gaba has heavier shots and a much better backhand than James. James hits flatter and cleaner. I think Gaba has slightly more power, and James has more pace on his shots. Their court positioning is also different, Blake stands inside the baseline, Gaba generally stands a little behind it.
It is definitely possible to play an all-out ball bashing game and win, but Gaba and Blake really aren't too similar in the way they produce their games.
If James really wants to get back to the top, he needs to get the movement/footwork back he's lost.
You don't get movement back as you get older. Blake is done, look back at 2006 TMC and see how beautifully he used to glide around the court.