Hm . . . what lvl are you now any way? ANd do you play any mod, or original campaign. For only those spells, and 14 intellect you cant be too far in game.
Difference between piranha and firestorm is aoe and type of dmg, so against demons/dragons piranha is much better spell, for plants firestorm ofc.
I dont know did you play before mage, but it`s normal to get around 60-70 int by end game, i had 91 int before and piranha are 7200-10500 physical dmg(all enemy units in first turn), firestorm 11000-11800 fire dmg to 7 cells area. Trap is 17000-25000 physical + poison, black hole 12000-21000 astral, illusion 108% . . . so mage is strongest with spells, but you need high intellect for it.
Of all hero classes mage have most difficult start, due to lack of spells and intellect, and no army because low lds, but later you`ll get to usual to battles 2 turn killing enemy army, and then spend 3-4 turns digging chests/reviving units if you play no loss.
But for that you need to survive till verona, and maybe kiting dersu/uzala/tekron to pick up exp spells and maybe some int shrine.
Good luck, have fun
