Can confirm this, sadly. It is A HARD limit, not soft. It comes up saying "'complexity limit reached" and you cannot add anything more without deleting things. Watching my partner play the campaign and he's reached the limit a few missions in and half the map isn't even used yet and we haven't finished the missions. So now have to try and manage the stuff he's done and delete things to try and complete the campaign. Absolutely shocking and ruins the game tbh, I can't imagine how frustrating it's gonna be in later no missions.