Well I assume the problems are due to it being P2P instead of Server hosted. I don't know how well P2P would work with a MOBA. Honestly the idea of it just screams "host advantage." Probably to the extent of Gears of War 2 patch 1. Because host advantage in a MOBA means that you get the first spell off, so you can finish your combo before the other player even knows what happened.
Plus P2P has to be well regulated. If someone enters a game with a strict NAT, they are just asking to get disconnected. If you have 10 people in a game that requires balanced teams, there is a high likeliness someone is going to have a strict or moderate NAT and will screw their team over.
There's a massive issue when matchmaking with a party.
The party won't follow you into the match. The party won't be on the same team. And matchmaking with a party can take easily over 15+ mins (a mixture of 2-3 mins) of searching before even possibly getting into a match.
I'm sure it's patchable, however Custom Games is the only sure fire way to actually play with another person.