For both of those questions, you won't like my answer.
When asked who was stronger, Thor or the Incredible Hulk, Thor and Hulk creator Stan Lee did not give a definitive power scaling answer that makes sense. He said that it depends on who writes the story. If the writer is a Thor, Thor will be stronger. If the writer is a Hulk, the Hulk will be stronger. Basically, whatever story the writers want to tell, they won't follow some set power scale. They'll write whatever makes more sense for the story.
Should you interpret Goh getting strong Pokémon as the writers just handing out strong Pokémon to the new guy when he shouldn't have them? Could Goh's Pokémon keep up with more experienced Trainers? That entirely depends on the needs of the story. If the writers want to tell a story that makes Goh look really cool by fighting an Elite Four member and winning, then Goh's Pokémon will be strong enough to beat the Elite Four member, even if Goh is using strong Pokémon he hasn't used in battle before. If the writers want to write a story where Goh uses all of his strongest Pokémon in a battle and loses to some out-of-nowhere strong guy we've never met before, even if Goh's Pokémon seem like they should snatch the win easy, Goh will lose even if it makes no sense.