This is how the Galar gym system works:
>each typing has a gym
>gyms are split into major and minor leagues
>top 8 performing gyms are put into the major league
>major league gyms get to be in the champion's cup, giving them the opportunity to challenge the Galarian champion
>minor league gyms can challenge major league gyms to replace them
>as a result, minor league gym leaders keep training in order to defeat and takeover a major league gym's spot, while major league gym leaders keep training in order to protect their position and defeat the champion
Other things to take note:
>Raihan is rumored to be so strong that if he moved to any other region, he'd be able to defeat their champion and replace them
>despite this, he's never been able to defeat Melony (implying she's also champion level, or close to it)
>in Shield, Allister canonically beats Melony
>all the gym leaders are trained by Mustard, a former Galarian champion who retired undefeated
TL;DR: Allister could probably wipe the floor with any non-Galar gym leader. He'll keep training and will probably end up champion level by the time he's an adult.
