It is my biggest complaint as well.
It is a natural consequence of teaching skills to students on their knees. If the students are not overweighted, they will be very tippy and off balance. If you want them to perform the skills easily, you need to pile on the lead.
When I posed for the pictures for the PADI article on teaching neutrally buoyant students, I had not taught on the knees for a couple of years. I had to pose for pictures doing skills while neutral/horizontal and while on the knees for contrast. I was wearing a shorty in a pool, and I customarily was intentionally overweighted with 6 pounds--I could dive a shorty in fresh water with no weight. When I was done with the first neutrally buoyant skill, I tried to go immediately to doing it on the knees, but I couldn;t--I was too "bouncy." I did all the neutral pictures first with 6 pounds and then took it up to 12 pounds for the pictures on the knees. In summary, I had to be 12 pounds overweighted to do the skills on my knees.