Here are 3 personal stories about operators matching divers by ability.
1. I was diving with an operator with multiple boats in Cozumel, and one day my boat had four divers: A husband and wife who were both DMS, a complete beginner on his first dive trip, and me. When the beginner ran low on air on both dives, I ascended with him to the surface, and then redescended to join the rest. After the dive, the operation owner contacted me to apologize for putting the beginner on the wrong boat, and she refunded me the cost of the dive.
2. On a trip to Cozumel last year (different operator), my friends and I were put on a boat with extremely experienced divers, and we had a week of outstanding dives in remote locations, some of which I had never heard of despite many trips to Cozumel. We only saw other dive groups on a couple of our dives.
3. On a big boat in Kona, Hawai'i, we were divided into three groups. Our group was told we all had more experience than the DM trainee who was "leading" the dive. He was mostly just getting to know the sites, and we were free to do what we wanted as long as we stayed roughly together. We entered the water before the other two groups were close to ready to splash, and we surfaced after the others were back on the boat and had gotten out of their gear. I wondered how many advanced divers were in those two groups because they had hidden their true certification levels.