I'm quite sure many will agree with you that the game's MP is quite broken. But whether someone considers MP as a core aspect or not can be subjective. I consider Civ 5 as a SP game with optional MP which makes its lack of MP polish tolerable. If MP was broken for games such as LoL, HoN, or SC2 I would've called them broken without a doubt. On the other hand I don't mind at all that LoL has almost no SP aspect for example.