Generally speaking I consider the duties of a DM to be a tour guide and to deploy the SMB at the end of the dive. Most of the time they'll say before the dive to begin your ascent at 700 psi or whatever and do a three or five minute safety stop and they'll usually say what the deepest part of the dive will be and how long they expect it to last. I agree with RayfromTX that we need to be responsible for ourselves. One time the DM, before the dive, said there was a lot of boat traffic (Cozumel) so don't surface until he deploys the SMB. Well, I ran out of air first and went to 15 feet, waited three minutes, and he hadn't sent up the SMB. So I waited, and waited, and waited and he finally sent it up. When I surfaced he told me he would have to take the valve off the tank and clean it because it only had 200 psi in it. Needless to say I didn't tip him for that day. Now I carry my own SMB. My girlfriend, who is OW certified to 60 feet and has about 22 dives felt uncomfortable recently when the DM said we would be going as deep as 90 feet. Even though she had been to about 80 feet with her instructor (after certification) she still felt uncomfortable. I told her she didn't have to go that deep if she didn't want to and could easily keep track of the group and DM from 60 feet (Cozumel) and, of course, I would stay near her at all times. It's supposed to be about having fun.
In any case we are all certified divers and are supposed to know what we are doing so, IMHO, we should be watching out for ourselves, stick to our dive plan, not exceed our comfort level, watch our computers or watches, depth gauges, and dive tables, and be sure we don't exceed our NDL and do the safety stops as we think we should do them. My girlfriend and I are in our mid-60s so I knock about 20% or so off the NDL for any given depth and if I've been down to 90 feet I'll add a couple more minutes to my safety stop. So far I've only seen the outside of the hyperbaric chambers and wish to keep it that way.
In your case you had an agreement with your DM to be watching out for you and he apparently deviated substantially from the dive plan. I would call this particular arrangement a "refresher dive" and I would expect him to be keeping things at the agreed level. If you paid extra for that I would request satisfaction in the form of a refund or an additional dive (two words that might get their attention are "review" and "TripAdvisor"
). But the reality, from what I have seen, is that many divers expect the DM to baby-sit them and many DMs expect divers to take care of themselves. So far nobody has told my girlfriend that she can't dive below 60 feet because she is only OW PADI certified. Maybe they've seen her log book and know she's been deeper
Even on one of my girlfriend's Discover Scuba dives they took her well past 40 and through some fairly long swim-throughs. But he literally held her hand the whole time and made sure she was 100% OK, except perhaps when he laid down on his back and blew air rings. Maybe your DM saw something down there that he thought would give you a thrill and to him that was more important (in the form of a bigger tip) than your original agreement. With so many great dive ops on Cozumel I don't see why anyone would risk bad reviews.