Also, if you like nature magic, consider this: whoever has the strongest nature magic/income in a game, will get to cast Mother Oak. Whoever casts Mother Oak, will have nature gems to recast Mother Oak, which means they'll constantly have a free 10 gems per turn every turn for the rest of the game. Gotta use diplo so people don't team up on you tho.
Well EVERY path has one of those, so its hardly competing. And frankly that is one of the low end income globals.
The way that research works is that each level in a school costs twice as much as all the levels before it combined. So, 50>100>200 etc. research points. Mother Oak being castable on level 5 alteration means that A practically speaking its the earliest sane global to come out every game and B the fact that you get it earlier means it generates more gems. Its "worse" than the other gem gens but its still the most *important* gem gen because of its accessibility compared to the others.
Admittedly this is the exact opposite of my problem with combat magic. Specifically all I really USE is the "one competent mage casting key spell" and don't really have the know how of when/how to use mage swarms. Actually I have issues GENERATING loads of mages for anything other then research monkeys, so that's probably a significant portion of that.
The truth of the matter is... it hurts your economy to put out mage swarms for combat. But its such a good strategy, at least early on, that you need to do it anyway. You really only want to have one or two mage swarms out a time for your first war. For the first, I dunno, three years, you ideally be recruiting a mage at every fort every turn, and get 2-3 forts up quickly to facilitate that. From there, think of your mage force as something akin to a medieval levy. Their primary value is economic, AKA sitesearching and research, you only send them out to war if they'll save you money by taking territory or preventing territory loss. You want to minimize the number of mage-turns spent at war, while having as many mages as possible in the important fights. So seek out fights with your mage swarms, don't pay them to passively patrol your territory or something. You also want troops that don't overlap with your mages. So if you're using evocations, you want the cheapest possible wall of units between the enemy and your mages that won't route. If you're using buffs, you need melee units that can do damage in melee, or all you're doing is delaying the inevitable. If you're using summons, a huge wall of infantry will actually prevent your 100% expendable combat summons from reaching the front while your troops you paid gold or gems for die in their place. Ect. Ect.
The other trick to mage swarms is you want to find a spell that scales 1:1 the more you cast it. Fireballs scale 1:1, one fireball does one fireball worth of damage, two fireballs does 2x as much damage. So do battle summons, almost, unless you fill up your front rank at which point their usefullness drops. But buff spells and debuff spells don't scale, because they can only be cast once per unit. Six guys casting barkskin is not six times as good as one guy casting barkskin, if you get my drift. You also just want to find a spell that's sort of overpowered for its path cost; easiest way to do that is quick SP experiments or internet word of mouth.