i am not sure i would agree 100% with the statement that "all respectable ops vet divers". i guess it depends on what your definition is of "vetting".
in all the years i have been diving and travelling, i think the only shop that ever "required" a check out dive for example, was on in st maarten. if you booked the shark feeding experience, you had to do at least one dive with that shop in order for them to gauge if you would be a liability on the shark dive.
other than that, it has always been the usual questions and/or form to fill out. when did you dive last? how many dives do you have? can i see your c-card? etc etc.
there are a small number of shops i have used that required an advanced cert before they would agree to take you to certain sites. none of these were in cozumel. and an adv cert does not prove anything. my wife has no other certs than ow and she has never been denied access to any dive site.
i think when it comes to vacation diving, and in particular in locations where strong currents can be present, there are two important things to consider.
1 - the diver has a responsibility to themselves, their buddy, and the others on the boat, to make an honest assessment of whether or not they are ready to dive in certain conditions.
2 - the dive operation also has a duty to make sure divers onboard understand what the conditions are, how bad it might get, and possibly describe what to do if conditions get so bad the dive should be aborted.
the fact is that many divers (even if they are very competent) have never experienced extreme current let alone what people like to call down currents. it is not really fair to expect any diver who has never been in these type of conditions to be able to understand how bad it can get and how to deal with it.
my wife's and my first dive on santa rosa was a complete sh*t show. we had no idea it was going to be as bad as it was. it was a horrible dive for us and we decided to cut the dive short no matter whether we had to leave the group or not. we were just not prepared for it. it was quite the learning experience for us both.
i cannot recall ever having any dive guide ever saying anymore than..."the current is strong today" and/or "the current is running north to south today" etc.
i am certainly not saying anyone is to blame for this particular tragedy, just reminding people that the ocean can be a very inhospitable place, and for those who have not personally experienced how quickly things can go sideways, it is hard for anyone to know how they will react.