>>34683158An older rival who has 5 level 50+ Pokemon in your first battle. The game doesn't expect you to win and, in case you somehow hack OP Pokemon for the match, gets a story cutscene that ends the battle with your other friendlier rival calls off the match.
You face the rival several more times in the story like this, and once more right before the E4 where the game now expects you to win. Every time the rival always has the same Pokemon at the same levels, thus the player feels like they have actually grown as they do progressively better each time before finally taking down their rival.
It also lets the player feel empowered right before hitting the E4.