Ideas and suggestions.

Diplomacy settings are configured in templates. In Anarchy and Clash, it works at full capacity, and no one prevents you from creating your own templates with your own settings (including disabling monster joining or choosing some other, non-standard combination of settings). If we are talking about G+U, then these are templates for single-player, not adapted for online play. In single-player, diplomacy is also overpowered, so it is toned down there. And there is no limit on the battle length. If someone creates a G+U version for online play, they will be able to set the diplomacy settings as they see fit.