I was diving for a week in Cozumel with a very good DM/Instructor who tries to improve everyone's diving - no matter what level. There are a couple of people on the boat who are diving overweighted and hoovering 120 cf tanks in 30 minutes. On the 2nd day we're crusing to our SI spot and the DM says to these folks that he feels that as an Instructor he has an obligation to his drivers to try and help them. Then he says that obviously they know how to breathe, but it is time they learned how to breathe like scuba divers (one of them had been diving for 10 years).
I think I would have been mortified if he had said that to me in front of other people. I would have probably skip-breathed on my next dive and passed out just to show him.
One of the hoovers tried to justify it by saying he was a big guy and used a lot of air. The other one looked kind of sheepish. Yet, the DM kept working with them, taking weight off and tweaking their gear so by the time our trip was over, they were able to keep up with the rest of the group in air consumption and were diving more or less horizontally instead of vertically.
Do you think the DM did the right thing? I personally think he should have had a talk with them in private. And yet I think he did them a huge favor by making them better divers.