I have avoided getting into the whole issue of whether the DM is hired as a a guide or a protector (or whatever). But in my opinion, if you feel you need a DM with you to keep you from getting lost or killed, then maybe you should not be on that dive in the first place.
I have been on Cozumel dives where the DM escorted someone up and others remained below. The DM let us know he/she was going up to the boat and on one occasion told us which direction we should head in the meantime. I don't think any of us gave it a second thought. I have also had occasion to ascend with a buddy while the remaining divers continued, either using the DM's smb or floating my own so the boat would know where we were. It too was a non-event. Clearly there are some conditions in which it is important that the group stay together, but those don't include an individual diver being unable to safely dive unsupervised. I expect to take care of myself on a dive and not rely some DM to protect me from myself.
If you don't feel you can safely continue or end a dive without a DM near you, then you need to reevaluate the wisdom of making that dive. Obviously, I hope, I am not referring to a situation in which a diver has gotten injured or become ill on a dive, or a sudden emergency has arisen and there is a need to get the group out of the water or away from a hazard, or students, brand new divers, training situations, etc.
Some ops, like Aldora, have a policy that everyone ascends together. Fine, that is their policy and it may well be safer and I have no complaints or criticisms of that procedure. I suppose if a diver feels that they are only safe in a group and when accompanied by a DM, then they should ask about such policies before booking dives.
Where is the diver's "buddy"?? That is what they are for and should not pass that responsibility to anyone. If they do, then they have no buddy! If my buddy needs to ascend, my dive is over! It's that simple... No questions asked.