I don't think it was a mistake, it just wasn't integrated that well.
The fully human fighters should've never been as marginalized as they ended up. The Dragonball-verse was diverse enough that they could've found something to keep the humans even with the Saiyans.
Playing: DC Universe Online(PS3)
Watching: Fringe, Person of Interest, NCIS, NCIS: LA
At least 15 percent of the moviegoing audience experiences headache and eyestrain during 3-D movies. I'm one of them. And no, I don't need corrective eyewear.