This is a very interesting question but there is an assumption behind it that we need to put on the table.
Namely, the assumption that the dive-guide should be responsible for the dive-profiles of all the certified divers in the water with them.
Is this so?
To my way of thinking, a dive-guide should be responsible for two primary things:
1) navigation through a site as experienced local diver
2) tempo, meaning in most cases that he chooses a 'line' through the site that works in terms of air consumption and duration that the divers with him can reach the exit with a reasonable reserve in their tanks.
Normally the dive-guide also gives a briefing in which he/she explains, among other things, max-depth, duration, entry/exit, what you'll see, some basics of the route and some emergency procedures.
These are NOT intended in most cases as parameters to ignore after which the guide is blindly followed to the tune of "just keep swimming, just keep swimming" in which you relinquish all responsibility for your own dive-plan and/or safety and put yourself in a position that the DM (despite how good they may be) is responsible for thinking FOR you.
To the contrary. If you are not planning your own dive, taking responsibility for your own dive profile and ensuring that it fits within the parameters laid out for the dive during the briefing, then YOU are the big-red-dot on the radar, and not the DM.
I'll give you two examples.
1) a dive on Elphanstone reef in Egypt (many people know it). It's a vertical wall with a hard-bottom at about 300m depth. We dove there with a guide whose instructions were "dive-time is 60 min" and "stay within visual range" (we were all experienced divers with a min of 500 dives)
One dive team (mine) decided to dive the reef shallow and look for Oceanic white-tip sharks, which are often found in the shallow range. We planned our dive as a no-deco dive and were ready to ascend to the surface after 60 min
Another team decided to look for hammerhead sharks, which are often found at 70-odd metres. They dove to 45-50 or so and spent about 15 min looking for sharks. They had a planned deco-obligation but were also ready to ascend to the surface after 60 min.... according to plan.
The dive guide did a dive of about 25m so he could see us in the shallows and see the other group in the deep and control the parameters of the dive. He communicated to all when he wanted the group to re-assemble and remained in constant visual contact with both dive-teams, in particular for tempo and navigation.
After the dive, both teams had achieved their goals and spotted their intended targets. Everyone had a safe, enjoyable dive and everyone kept themselves to the general dive plan. Isn't this *exactly* what you expect from a dive-guide?
2) A dive I did in Mexico many years ago. The dive parameters were "45 min", "dive within NDL's" and "don't forget to do a safety stop".
There were 3 or 4 buddy teams, which mostly consisted of inexperienced divers. The DM went overboard and most of the boat went overboard with her and started swimming where-ever her flippers went. The DM decided to swim at about 10m through the dive-site.
I, and my buddy,... however... decided to decend to 30m (the hard-bottom) to look for nudibranches on the sandy bottom. We were fully aware of the parameters of 45 min, no-deco and and safety-stop and followed those instructions to the letter.
The DM, however, didn't understand her own briefing and started getting spastic as soon as we got deeper than about 15 metres. She whistled us back 3 or 4 times because we went deeper than she did and started inspecting our SPG's and giving us increasingly "stern" warnings to maintain depth.
We exited the dive somewhat..... er... irritated... because the DM wouldn't accept us doing anything else besides following around behind her flippers (which is the only thing most of the divers on that dive saw).
On this dive: (a) NOBODY saw what they wanted to see...unless the objective was to look at stupid pink jet fins.... and (b) nobody enjoyed it.
However, she *did* control every variable to the point where she was diving for everyone in the group.....
...
I *do* believe that in some situations it's important to control the dive to this extent, but outside of a course format those moments are rare.
R..