If he was crazy strong, we wouldn't have known that until after the tournament; nothing significant about their power was noted after that. Vegeta desired the majin spell based on Spopo's tournament abilities and Goku's description of majin Spopo (beyond his natural abilities) is perfectly in line with the spell's effect. If he's way strong, either the majin spell affected Vegeta differently or Spopo has crazy potential. Given that he was some average chum with a regular human body, I don't see why his potential was be anything significant.
The first guy to have an aura was enraged Gohan (I think); it would pretty bizarre for some random chump to have more, or even comparable potential to little Gohan.