I actually took the time to figure this out and put the greatly improved proportioning into a visual.
https://ibb.co/yQZy8kf
We know that we have to deal with a low amount of stats since they are what the heroes start with and a nice even fluctuation of 5 stat increments.
Let’s say that every +100% stats that a hero has over another, their size goes up by 25% comparably and this gets cut in half for every additional +100%. This would make the sorceress 37.5% smaller in scale than the Barbarian. But the image shows how ridiculous even that would be.
The image shows that upon adjusting the stats with this diminishing scale in mind, that the Barbarian, Assassin, and Sorceress end up looking both great and proper next to each other.
But in this visual example the Assassin dropped 15 energy to go up by 5 in Str, Dex and Vit. Sorc dropped 5 energy and 5 dex to go up 5 str and 5 vit.