Sounds like Blue Angel's approach is somewhere in between. I'm glad to see it described here, as for some people it's an issue in choosing a Cozumel dive op. (which says a lot about Coz.; it's got enough strongly reputable op.s that divers can get picky).
I was mostly joking. If you went in as their buddy you made that deal up front. That's just how this game is played. 40 minutes into the dive, 20 minutes or just 2 minutes into the dive. If your buddy has to call the dive, you both call the dive. No questions asked.
You may have two pairs, each being a big guy and his petite wife. If one of the big guys runs low fast, the DM might assume the other big guy is next lowest and send the two big guys up and let the ladies have a long dive. And he is probably right though there are exceptions. But if you are requested to ascend with someone you ascend with them. If you don't like it, discuss it with the DM on the surface. At depth is not the place to have an argument about it.