>>56001312It's one of those things ruined by later retcons.
In the context of Gen 1, he wasn't just being cocky, he literally was the strongest, because the Pokemon League was just THE Pokemon League, the only one in the world. Come Gen 3, this is retconned into every region (except Johto, which is now the odd one out) having its League and Champion, making Blue retroactively much less impressive.