Although, 100% is quite overpowered.
Let's say we have two heroes developing at the same rate. One of them didn't receive any training and reached level 18 (which is normal for online play?). That's 57,533 experience points. The second hero received expert training almost immediately and has about twice as much experience, meaning less than 117,134, or around that number. That's levels 21-22. Essentially, the second hero has an advantage in that they have 3-4 more stats (in total) and 0-1 additional skill, but they paid for it with an entire expert training slot. In my opinion, it's not that bad, but I'm not sure if it's completely overpowered...
