I see him as every made in Toei character. He had the power the plot required at any moment.
In fact, Pikkon vs Goku is one of the worst fights when it comes to power progression. So we have base Goku and Pikkon both fighting more or less equally, then Goku turns into a SSJ and starts to loose without no more reason that "we have to make the fight more interesting" and finally that fire-technique that was beating Goku but suddenly Goku delivered a final blow like he did in every single Toei designed fight (while Toriyama always made sure that every fight was original, Toei always designed the fights following the same scheme -> Goku loses, Goku loses, Goku loses and when it seems that he can't win Goku wins the fight with a single final blow).
When I was a kid I always assumed that those in hell had their powers restrained somehow.