Ideas and suggestions.

In my opinion, the biggest weakness right now is the imbalance of magic schools, which is what worries most players.
In TES, a good solution was proposed: move Direct Damage and Town Portal to other schools of magic, so both water and fire elements became in demand even for the main hero.

It's unclear why they don't want to change it; it seems obvious to everyone that there's a constant "earth-hunting" and then "air-hunting," with fire being used situationally, and water rarely used. Moving Town Portal to water and Direct Damage to fire would really balance the magic schools. In return, any unpopular spells of levels 3-5 could be moved.

Added 12 minutes later

I agree. Also, increase learning to 20/50/100%, etc.

I would enhance it not just with additional experience, but by giving the hero additional Primary Skills at levels. The specific numbers need to be tested and balanced, but something like +1 skill point for every 4 levels at basic, for every 3 levels at advanced, and for every 2 levels at expert. (Giving a point for every level might be too strong, but overall, it needs to be considered).

Alternatively, additional experience + the ability to choose from 3 skills instead of two at levels (from 4 at expert?? debatable...). As a result, it would become a real learning system, allowing for more precise and correct hero development.