But can we even trust the cinematic trailer at this point?
No, we can't. It's a cinematic, it's just for promotional purposes.
The open areas around some of the objectives will make for interesting tactics, a team that doesn't work well together could really do badly when faced with a team that has everything down pat.
True, in general, main objectives are in open areas while side objectives are in smaller areas, making it easier for smaller squads or individuals to complete it. With the main objectives in more open areas, you'll need a bigger part of your team to complete it.
Oh and if you are sneaking up behind people, you should either have 1 shot backstab, or you aren't in the right place given the class you picked.
That's not true. If you can get in the back, playing as any class, you can pick off enemies before they reinforce the important places or you can just distract them. By killing 2 people in the back, before they can reach the main battlefield, you will get a lot of attention and they will not be focusing on the important things.