mmm, I disliked that diplomacy and interaction were treated like the same thing. Perhaps that's semantics though. Though Dominion has far more interaction than players initially realize, it could have more interaction without any diplomacy, for instance, a greater emphasis on attacks and reactions.
Interaction is just a potential source of fun factor though, and you're correct that it is not a standalone criticism, it's an "accusation in search of a flaw". I enjoy interacting in Street Fighter, and if Street Fighter had no interaction I wouldn't like it at all. However, if my favorite single player game were playable online in a simple, interaction free "race to beat the level" mode, I would enjoy that more than Street Fighter altogether because I really like the single player mechanics, many of which are impossible to adapt to an interactive multiplayer.