One time in Cozumel we had 6 ships. More important than the pure number of ships... is when your ship docks in relation to the others.
Ours was the last to arrive. We had rezzies for Sanchos. Everyone we talked to when waiting for taxi asked us. No worries.
We got there... and we were on the far, far, FAR end of the beach. Took forever to get any service, had any drinks brought to us, etc.
We ended up basically spending most of the day by the pool and just getting drinks from the pool bar.