I know this is far back, but I just had to comment on this post.
While you're right in some of the choices being quite odd, you also gotta take the other champions into account. The levels of his team far exceeds any other champion there has ever been, even though his highest leveled was a Pikachu. Also I'm pretty sure that he's not supposed to be Ash, however his team was based on the most popular Pokémon from the first generation. The game had been long overdue, and I think the game developers wanted to put something in that would remind the players of the first generation, so they made a team based around the popular Pokémon from that generation. Pikachu, being the mascot of the whole franchise, should be his main Pokémon. The fully evolved starters were some of the most well known Pokémon from back then, so of course they should also be in the team. Both Snorlax and Lapras were strong event Pokémon, where you couldn't even get through the game without beating Snorlax, and you were also most likely to get a Lapras along the way from Silph Co, which made both of them pretty well known too. So yeah, while some of the second generation Pokémon might've been more ideal, it just wouldn't fit into the whole theme.