What I really think is causing people to whine about certain demigods being OP is simple: Lack of necessary multiplayer teamwork tools. No, I am not pulling things from my ass, I think what is holding this game back is a lack of a few necessary multiplayer functions such as VoIP, a better pinger, and a community-wide mentality that this is a 1vs1 game because of the way the game is presented. Teamwork wins here folks, no matter what Demigod you are and your enemies are using, the team who coordinates is going to win.
However, this game lacks VoIP. SO what happens? Most people just can't type fast enough or coordinate well enough using chat, so they end up going off on their own and then getting killed. Then they come back to the forums with "OMG OP DG".
A stronger multiplayer suite of teamwork tools, would, for the most part eliminate alot of the bullshit around here, because it would rest on who is the better team, not who is the better 1vs1er. Even a newer player would benefit more from this, because they could easily understand his teammates and not be thrown off by the quick, seemingly mean tone, that using the chat function can sometimes do.
Certain demigods ARE better at 1vs1 fighting. That doesn't mean that particular demigod is more powerful, it just means it is better at a 1vs1 situation. However, if teamwork is factored in and coordinated with characters like Sedna and QoT, who are extreme support characters.... it changes the dynamaic altogether. There are so many amazing combinations of Demigods, that used together as a team, create much more brilliant results than what any powerful 1vs1 character is capable of.
This is a TEAM game... lacking teamwork features. I recommend people start using Ventrilo (for now). The quality of your gameplay experience will increase dramatically when working as a team. I hope GPG and Stardock implement stronger multiplayer features later on.
Teamwork would strengthen "support" characters. The reason why some Demigods seem more powerful is because they can be played more effectively solo, than other characters can.