[Gatts]

Calculation for Fireball:

Center Damage (3rd spell level):
x = 360 * (1 + 0.1*INT)*(1+0.1*{Int/7})*(1+0.1*{Destroyer + artefact bonuses})

6000 = 360x {INT and other bonsues}
6000/360 = 16.6
Let's say you Have Destroyer on MAX -> so your sinergy bonus is only 11.06
11.06 = your INT sinergy bonus
That means your INT is equal 53

Havin INT 53 is quite over average, right? - but 6000 DMG in centre of Fireball is totally not what would make you win battles on normal or higher difficulties - not without making effort on strategy planning... I normally have most of the game on impossible INT below 30... first with Xeona I start to increase my INT rapidly - still leveling up the staffs so they will give +5 INT is HARD and beating 4 stacks of 180 archmagi and 4 MAD GREMLIN towers with 8000 HPs and 2 stacks of 400+ Inquisitors and few Priest stacks of 800+ ... sometimes there is one stack of 1600 archers... well - how would your 6000 DMG fireball help you?

And sorry for misunderstanding you quest comments - you are totally right - there are less quests as you are near the end - maybe due the fact that devs want that the player will focus more on the MAIN quest ...