If you are going to have a specialist there need to be challenges that are tough for them. Those can be level 23 challenges instead of 20, but that leaves us in a pretty similar place. Right now the band between Trained and Legendary is 6. That's quite large in PF2 given the way critical success and failure work. Maybe it should be less, but I'm not sure how to make it less impactful without making each step feel too small. Maybe the band should be trained to master.