I don't think these enchantments are over the top, at least not in this case.

They make for a nice strategic choice, actually: on the one hand, I get some awesome mages; on the other, I sacrifice a fair bit of research and mana income, the mages take much longer to train, and they miss out on fortress accuracy bonuses. I also have to micro-manage the enchantments, so these mages are far from hassle-free.

Three-essence spots are very rare in the wild, so a three-essence fortress is unlikely. Even with two essence, you can't get both bonuses and still produce your mages before the heat death of the universe - you need a slot for hammers/set in stone to speed things up. Not to mention that with just one or two essence, these bonuses are a lot less exciting. 

Arh, well as you understand I disagree

Sincerely
~ Kongdej

I have been using Aura of Grace to make ridiculous ranged units for awhile now. Once again the problem is the exponential growth in the effectiveness of essence. Also why fire but not lightning and cold?

I guess if the other enchants that are available to me weren't as strong, I might consider this strategy excessive, but to be honest, I prefer my choices to be significant. Trading 20% of my research and mana income over a few turns in exchange for 10% attack boost on a single unit is boring, and I probably wouldn't even bother. Make that 100% research in exchange for 50% bonus and dual-element damage, and you have my attention.