How to *objectively* balance the game
Players whine, numbers don't.
If I were GPG I would log (at the end of each game) all ingame decisions like which item gets bought how often, which Demigods and which skills are chosen. All items in the same price class that are bought very rarely by the gamers are apparently not worth buying and should be buffed/changed. Same goes for skills.
If that is too complex, I'd just look at the already available win/loss ratio of each Demigod and balance accordingly. The win/loss ratios are already okay, but for a competitive game like this they should be 50% ± 2% at most. Perhaps the easiest way to balance is to change the Demigod's stat improvements or mana costs of skills.
That would balance the game as objectively as possible, which is very important imho.