foo, since I was in that game with you I'm going to comment a bit on this.
First off, this game is not about 1v1. While Erebus may have a tough time killing a QoT minion build, there are other demigods that can, and she will almost certainly die if caught in a 2v1 situation regardless of the demigod combination. Sure she can hold a lane against Erebus, but that is when we should have switched off or teamed up against her (however, our UB was an AI after the first 3 mintues I believe).
Second, saving for and buying some cleave items and the consumable anti-minion item would have helped (I can't think of its name right now).
Third, she was built for survivability. She was doing shit for damage the entire match, but could easily take a large amount of damage. By late game she was using shield and HoL, and as such was nigh unkillable in a 1v1 situation.
IMO, Erebus is fine. His damage output is still great and his self-healing potential is still awesome. Mana control with him is a tad trickier since the rebalance, but still very managable (it used to be possible to go on huge killing sprees without having to visit the crystal for mana or use mana pots). Not every demigod should have a counter for every other demigod, otherwise why do we need teams in the first place?