I have played with groups of 6 and not once has anyone complained about loot amount. We usually dont go through the same POI, so its not an issue, unless we all join the same quest, and even then we all get our own loot at quest completion.
If you aren't a fan of moving through a city to get to the fresh POI, I can see this being an issue, but honestly as it is, SP with 100% loot feels way to easy to me.