My proposal is to increase the chance to level up the special skill only for 3* heroes.
Right now is way to easy to reach the top level for this kind of hero and let the special behind.
Differently from 4* and 5*, they are one ascension short, much less levels and much more easy to upgrade.
Even using 10x heroes of the same color every time, the chance to get maxed and have to use other heroes only to level up their special is really high.
So for me is kinda fair to increase (leave to you how much) the possibily to upgrade their special with normal training.