I like Heatran!
I always imagined that it started off as a weak Pokémon and the toughness of the mountain and the area made it tougher and tougher until it eventually became the most powerful there. Not to mention I love that part of the game for some reason. It always reminded me of Death Mountain from the Ocarina of Time.
As for Pokémon that I'd 'get' rid off, I'd have to agree with Burmy. Cool idea, poor executed.