After you reach champion level 100 for any class there is no feeling of progression for this class anymore.
Maybe extend champion levels up to 1000?
The easiest thing I can think of it’s +1
to either: armor+health || magic || attack
(armor+health +1 to both, to make it on par with magic and attack)
on levels 250, 500 and 1000 for all classes equally.
These levels are difficult to achieve, but there will be a feeling that you are aiming for something, and you don’t win in vain with the maxed class.