I'd read this thread a few days ago, but did not reply. Happen to be back here and thought I'd take the time to give my opinion.
First, a lookout on the boat is required by the Port Authority. This "clause" was grandfathered in shortly after "9/11" and a lot of discussion was had. It was not long before that small operators were booming, and if you owned the company that had only one (1) boat, you were a do-it-all and at most, had one employee.
With the "clause" taking affect (and it had evidently been in place for eons, but never enforced - it just all happen to coincide with 9/11), you were required to have someone "up".
Prior, and maybe even today, if you have a boat of six (6), you. probably feel more comfortable underwater with those divers. You have control of their well-being.
Today, there may be that rare occasion that the boat may have to be left unattended.
Is it a common practice in Cayman - absolutely not. Having been here (in the industry) for 25 years, and having been diving since the late 60s, I will put Cayman's standards against anyone around the globe. The dive ops on this island do a damn good job and don't you ever doubt that. We try and help out one another, work together and make it "right" for our customers.
If you are not happy with the company you are diving with, believe me, there is another one nearby that will sure be happy to work with you.