Don't feed them. Problem solved

Well, the feeder is usually not on my team, I'm the one taking advantage of it. Anyways, since you don't see a problem, it is probably not an issue.

This. As in many strategy games, the costier things are here to make you able to finish a game, so there is nothing wrong with them being powerful.

But feeders are indeed a pain, maybe modifying the system would help: let's half the gold gained for a kill and make the demigod that lose the other half of the gold.

Feeders would be less problematic that way, loosing all their gold will make them change their way of playing and their teams would only suffer from an useless ally and not from overpowered ennemies.

Yes, my experience is if you spend your gold on getting good items, you can kill the enemy DGs "how many times you want", giving you plenty of gold for giants as well. This may not hold in high-level games though.

Artifacts are there to end the game. But seeing as how the problem is the game ending at 15mins sometimes, then maybe each artifact should have a timer to when it becomes available for purchase? This could also be an adjustable game setting with the option of no timer to very high timer.