As I see it, there are several options to reduce the potency of spells without making them unworthy to use:
- Increasing spell cost. Now spells usually cost 20 mana per cast. Maybe raise it to 30 or 40?
- Delay the promotions that increase spell damage. The first of these might require min level of 4, the second might require Channeling II (so Adepts can not get it), the third might require Channeling III (so only for Archmage).
- Increase the cost of Knowledge of the Arcane.
- Increase the herb cost for arcane units.
- Make various resist promotions easy to get (reducing prereqs of these, more protection from combat auras?).
- Make some armors grant (small) protection from the elements. Some civ specific armors already do this, but maybe medium level armors should too?
Personally, I prefer increasing spell cost, making promotions that increase spell damage harder to get and increasing resist from combat auras but I'd love to hear feedbacks.
I like all those suggestions, the only problem I see with armour/promotions is: would the AI really make good use of it? As it stands right now, it seems to be completely oblivious to the power magic possesses. So I guess increasing the cost would be the more effective way to do it, because it would put the handicap where it matters, on the human player. The AI almost totally neglects magic (apart from summons), so the armour thing would hardly effect my playstyle, only theirs.
I got some more ideas to add to the pool:
1. Add a (short) cooldown to any offensive spell except the basic attack (magic missile). So low-level spells can only be cast every other turn, mid-tier spells every 3 turns and so on. That way you also slow down the XP gain, because magic missile doesn't give any. As it is right now, spellcasters level up insanely fast, because they gain 3XP per hit (up to a limit of 40XP), whereas non-magic units only gain 1XP (per kill). I'm playing with slower XP, the ratio is probably different without it.
2. Limit the damage spells can do in a siege. Atm you can completely destroy a city garrison by using magic. Make it similar to artillery, where you can't damage the defenders beyond a certain threshold. The percentages could get higher the more powerful the spell is. Low-level spells have a limit of 25%, the top-tier ones can damage up to 75%...maybe?
3. The main offender in terms of imbalance is still the "Sorcery Discipline" promotion. It increases the number of spelltargets by 100%...one hundred percent! That's the equivalent of the Blitz promotion for non-casters. The difference is, whereas Blitz has a minimum level requirement of 10, SD can be attained by an adept as soon as he did aquire 30 XP. Which, because of the very high XP gain (see point 1.), can theoretically be achieved 10 turns after you first got him. That's out of line with the discipline promotions that any other units can take at that point.
This has to be reduced at least to 50%. Because at that point, you pretty much don't have to care about your spellcasters promotions anymore, it's really all they need to be absolutely devastating against anything.
So that's it. I'm not saying that all these changes are necessary, but taking care of number 3 would probably reduce the disparity between casters/non-casters by quite a bit.