I don't know what the problem with the lighthouse fight is...
I killed them all in three turns without any losses.
The fight against Braccus court of sceletons in the far east was much harder imo, the hardest in the game. But then I met them at level 5 and the lighthouse party at level 10. Guess why my experience is different than yours. For me the lighthouse fight was really a cakewalk...
But nevertheless I agree with most of what was said here about balancing in general.
Another suggestion:
Again me - as a fan of D&D and of the omnipresent mage as Stabbey might call me - I would vote for more deadly spells that have a low chance of succeeding. Not only for the player but especially for enemies. "Finger of death" or "entomb" are good examples from D&D. If they suceed one character has almost no chance to survive. Party members hit by deadly spells like "turn to stone" of "entomb" were even impossible to bring back by normal means or usual resurrect spells. The biggest con of these spells were that they were hard to cast and in most times the casting just failed. In that case the mage only waisted a lot of time, making decisions more meaningful and combat more determined by luck and dynamic behaviour instead of static "numbers games".
I know that some people hate games based on luck and percentages (this philosophical battle is even bigger in board and tabletop games) but personally, I'm a fan of that to a certain contect especially if it is connected in a meaningful way with other gameplay elements (not being able to save during fights is CRUCIAL to that!). And Divinity: Original Sin already has a chunk of percentages and luck integrated, namely for melee fighters. Every time you swing a sword there is a chance to miss the target. That - very very sadly - doesn't apply to spells and skills so far with is a HUGE hit to balancing. Everyone should be able or in danger to miss the target which means mages and rangers as well with every attack and not only melee fighters.
I fear that it is not even balancing we're talking about here. Balancing would mean that you have working system with the wrong numbers. But I fear that we have (partly) broken or non-functioning systems. In that case numbers don't matter because you would never be able to balance the game properly, to neither hardcore fans nor casual gamers... :-|
