Frontier Brains are implied to be Champion tier or high level E4. The Hoenn frontier is arguably implied to be the overall strongest(though individual members of other frontiers might be stronger).
Palmer is ranked above Cynthia in Sinnoh, but Caitlin is confirmed below both Iris and Cynthia(even after her timeskip in Unova).
>>52651810Scott also says this:
>"Hi, hi, <player>! You know that you can challenge the Pokémon League when you've collected all the Gym Badges? With your talent, becoming the Champion isn't a pipe dream. But did you know? There's somewhere even better. But that's all I'm willing to say for the time being. It's something you can look forward to. When you've won your way through the Pokémon League into the Hall of Fame!">"Have you met any of the Frontier Brains? Better yet, have you obtained any symbols from them? I handpicked the Frontier Brains as the toughest Trainers anywhere. But I'm sure that seeing how tough you are will startle even them!"Blatantly implying the Frontier is superior to the Hoenn league(and its Champion), partly because the Hoenn Frontier isn't made up of Hoenn people but people from all over the place.
>>52653504Gym Leaders at the bottom is mostly true, but in many regions there's at least one gym leader that is stronger than at least some of the Elite 4.
Kanto arguably has Koga(who is now Elite 4 in GSC), Clair claims to be E4 level(the question is whether or not we can take her at her word), Wallace is blatantly above the E4 in Hoenn, Volkner is on par with Flint, Cheren is confirmed to be champion tier, BW1 Iris and Drayden are arguably implied to both be stronger than the E4.
