The issue isn't even just the openness, it's the lack of controllable openness. Let's take Bad Company 2 for example. You could destroy absolutely everything, so you could say it was very similar in that enemies could enter from any location. The difference is that if that happened, you could absolutely level certain areas and create open sightlines from which you could fight and defend the area.
With the current map design, they're simultaneously too open in that enemies can come around any corner and there's no true chokepoints you can set up and defend, but also, not open enough, in the sense that if you could destroy and open them up more than they are, you could actually have an open line of sight where you can lay down fire.
The issue specifically is that in previous battlefield games, if you had teammates present in a general area, you could know with vague confidence that unless someone is an absolute G they couldn't sneak through your teammates and get behind you without you noticing. They'd have to win via fire superiority or through actually clever flanks. In the maps as currently designed, the presence of your teammates behind you has absolutely no relevancy on where enemies can come from. The enemy could be trying to just run into your friendlies, and because there are so many winding routes to every objective, they could still miss them by complete accident.