That would make gameplay very slow, and it would require a complete overhaul of the Ki-system. The Ki-cost of every attack, every move, would have to be adjusted, because you couldn't just regenerate Ki anymore. You wouldn't be able to use all the moves as much anymore, because it'd be much more difficult to gather up enough Ki. You couldn't swoop as much, fire attacks as much, etc.
So yeah, I don't think the idea would really help the game much.
Maby you havent noticed. But ESf is not true to the show nor do they want to be 100% true to the show. Heck if it was true to the show youd only have Gokus (who are imortal cause they cant be beaten) and Buus.
Besides In the show they had a fiew years in betwean enemies. In ESf you have like 1 second if you are lucky.