Not to mention the fact the whole game was built around the idea they were going to make it ‘multi-player’. Sad fact is they never went back and fixed anything after deciding against it. But yeah, it had nothing to do with the character being too powerful. In fact, I don’t doubt the hero could have been used in several more titles after that with how he was designed.
Well, as Dragonball showed us, you can always just recycle a character and use a more powerful enemy, so yes he could have been reused.
You can hardly compare a character like Goku to the Hero from QfG. In the QfG series they even had constant reminders there are far more powerful people out there in the world(That aren’t enemies no less), which means there is always more room for growth on a character.
All in all, I think QfG went the best route when it comes to making a character for a game you plan to continue on. Start them at nothing, and make them claw their way up. If you start a game series out with a godly badass, you’re pretty much dooming yourself for later titles from the beginning.