COOP's are a great way to simulate real BOB missions IMO, with a COOP you can have any number of planes in the mission depending on hardware of course.
You could have 50 bombers flying at 15k ft being escorted by 30 109s all flying in formation.
Your squadron of spitfires is made up of your mates from ATAG, and your all spawned at 20k ft together in formation 5, 10, 15 mins from the bombers, or you spawn on the ground for a scramble if you want.
You fly the mission and return to base as you would in real life.
Now imagine that