make everyone surface together...due to safety factors. There is so much boat traffic, that having anyone surface away from the group can be very dangerous, depending on the dive site. This is a disadvantage to diving with big groups.
I handle this in a few different ways AND my captain is always right above us.
1. If the diver is a new diver, they NEVER surface without a divemaster. For this reason, if I have a new diver(s) on the boat with experienced divers, I have a DM just for them, regardless of whether I have 4 or 6 divers on the boat. I want everyone to enjoy their dive.
2. If the diver is experienced, I will let them surface alone IF they have a signal buoy. I provide signal buoys for each buddy team if they do not have their own.
3. If the group agrees in advance for everyone to surface, then that's what we do.
Scottbeach, regarding convenience for onsite operators. Some of the convenience reasons you stated are not exclusive to onsite operators. For example, I rinse and store gear daily for my customers and I meet them on the day of arrival at their hotel to complete paperwork, so the $20 cab ride is not an issue. With a smaller operation you are also more likely to have the option (or at least a say in) which sites you dive. With smaller operators, the dive are decided upon the morning of the dive based on conditions and diver preference, not by a preset schedule.
Dressel has a reputation of being very restricted with their dive sites and only dive the southernmost reefs, which really limits your dive site choices. They have also been known to schedule certain days for certain sites, which is a policy that I don't particularly agree with because it restricts some divers from the dive and/or it may eliminate the option of diving a certain site for those that are only diving 3 or 4 days. For example, a diver arrives on Friday morning and will be diving Saturday, Sunday and Monday. They want to dive Palanar Gardens, but Palancar Gardens is scheduled on Friday mornings and Tuesday mornings...they automatically do not get to dive that site. Just some things to consider.
Like I have said before, there are many good operators (and bad ones) in Cozumel, so do not feel like you are obligated or stuck with the onsite operator at any hotel.
Have a great trip!