>>48866869depends
Remember, Ash himself was Recruited to be a Frontier Brain but he turned it down.
In game they always have EV trained pokemon with good IVs and are post E4.
If we take the E4 as government positions (which in game is fuzzy) the brains are the strongest trainers not working directly for the league. If the E4 are just trainer status then they aren't stronger than the E4.
You always fight the brains at a set level, you can always grind for the E4 so pound for pound the brains are stronger
