Right.  They are great when used with a mage... but mana limitations are so painful right now I don't see the point in using mages often.  Maybe I need more experience in the area.  But all of my games so far have resulted in almost no tactical spell usage since standard attacks just made more sense (and mana was so limited).

Being a spellcaster you reduce the mana cost of tactical spells by 25%. There are traits to further improve this, as well as items in game. Not to mention water spell Mana Tide (or something of sorts) which can be cast on heroes to reduce tactical spells mana cost by 50% (and has no upkeep is a one time cast for 50 mana if am not mistaken).

The more shards you posses and higher upgrades you give them (shrines, altars, temples etc) and more cities with essence resources and mana buff you have, more mana per turn your will generate.

Of course if you have more cities on spots with no resources, only 2-3 shards (basic building like in early game) you will struggle to chain cast spells in tactical combat with non-spellcasting heroes (even more so if you play with the dwarves - Gilden who got a 50% penalty to mana cost increase for tactical spells).

All hero abilities cost no mana in tactical combat, EXCEPT those who are spells (like racial spark, or flame dart etc). It makes sense for a spell to cost mana even if is a racial / hero trait.

Caster types get to shine mid-late game when you have more spells at your disposal and larger mana reserves (and they do overshadow other professions as is to be expected). If they were so powerful early game then would be no reason to do anything else but spellcasters.

Early game haste / blind / slow are all great low cost high return spells to use / abuse. Don't try to cast fireball 3 times a fight and you will be fine

Not to mention all those traits spells already have a 5 turn cooldown, like spark.

You don't have to use soulspark early in game, or when you do, you really don't have something else to cast (you already used haste and w/e else you had). It scales with unit progression and level of caster as well. It's not meant to transform your pariden soldiers into ranged spellcasters that kill stuff before it even gets to them. It's there as an option vs high armor targets, targets you don't want to risk a counterstrike from, or to finish off something that's running away etc,

Mana limitations? Build more stuff that gives you mana, put Meditaton on every city.. if you can't find enough mana you must be doing something wrong. Sure I run out of mana every other turn at the beginning of the game, but like any resource if you focus on it a little you'll end up with so much mana you won't know what to do with it.

Soul Spark is awesome, you can kill a banshee with a couple militia units for big xp right at the start of the game, any other faction is going to have to avoid it for a while until they get hold of something that can kill it. Or kill those bandit groups without taking a scratch on your precious earlygame units.. if it's not worth the mana cost to you right then don't cast it.. but there's plenty of uses for them. If I have a couple hundred spare mana and I find one of those larger sized combat areas I'll just hit autocombat and let the units all blast the enemy instead of going to the trouble of moving them down the field

No it doesn't, of course you may feel that way if you are not used to mage characters. If they would be freecasting all time non stop with no regards to a resource for casting spells, nobody would ever even try other specializations.

Am not joking. Plus there are some spell combos that are insane when used right, even in early game. Want to know how Empire of Resoln can fight tougher enemies and huge armies despite they have no access to armor past leather? Cast your familiar and keep him in army to get xp to increase his spell mastery from level ups. When you start a fight cast infection with Ceresa. Start spamming blind, slow, graveseal and curse on a single unit. If you have a widow cast beguillle as well. Put infection on that unit when it finishes casting. Result? All enemy units are now blinded, slowed, taking critical damage from all attacks, and have no defense, with 50% chance of attacking their own units in melee. So with ~60 mana you turned a super army that would have squashed you, into a walking parody. This is how I can beat with Ceresa a huge troll army with 4-6 beasts and 4-6 trolls with only a militia, spearmen, sovereign, widow spider, familiar and a shadow wolf in early game (note 2 units are summons, all I did was training a spider in city). So with an army with ~100 hp and 80 atk you destroyed an army with 300-500hp and deadly atk.

i think spellcasters aren't too bad in the early game actually. the thing with spellcasters is- all (?) the premade spellcaster sovs and most of the mage champs have more than one school of magic available; and more often than not, one of those schools is water or air. both of which have cheap and useful spells at level 1 (slow/haste) that give you the upper hand in early fights without draining your mana.

keep that in mind when you make a spellcaster sov - if you want them to feel somewhat useful early on, don't go all out on warlock/brilliant/adept/staff of souls and fire apprentice. not saying this a a bad setup - but it will be very weak early on. skip some of the traits and pick up something that helps early if you don't want to wait until level 8 or something before he/she feels useful.