Hey guys..new to this thread so sorry if I repeat something.
First issue .. there are too many many types to make them all really usable and some are certainly better than others. When I play, my archmages are almost always going for nature magic to adjust the terrain especially when I play a Non-Erebus map. After that is usually enchantment to make my soldiers that much stronger. Body Magic is next for Haste and Regeneration.
Summoned units maybe good in a pinch or scenario, but I prefer units I can keep around and make stronger over the length of the game (soldiers, archers, etc). This eliminates alot of the magic mana types.
Some city spells like inspiration, hope, and those are nice but they're something I might use when I have enough soldiers to defend my city. Their utility is fairly small.
Life magic is good if your fighting a nation that uses lots of undead units (Sheaim, Scions, Hyborem). Being able to destroy an entire stack of undead with just a few mages cripples these nations, but after that, they are not useful for much.
Only reason I chase every magic type now is to have the ability to make the Tower of Mastery as a victory type. I chase all the victory types when I play.
A reduction of mana types might help improve some spell lines and eliminate those that really dont have alot of utility.
I'll use another post to keep this going. I don't want to write a book in one post