Agree, the effort it takes to set up an ambush is considerable. Party members wandering off and blundering into combat.
Stealth is also weird. If you start a fight with everyone in stealth, you have to manually activate them in the initiative sequence, otherwise they are skipped by default. That's clumsy. Most people are going to want to get the drop on their foes to start a fight if possible. The game makes that very awkward.
Yeah, there's that too. I can sort of guess why they did it from a co-op point of view, but it seems to work more often against you than in your favor.