it can be. but it can also be an equipment problem.Floaty feet is a skill problem
but i completely agree ankle weights are not the best solution. i have had trim issues in the past and have used ankle weight many times.
they helped me at the time but i had to learn to solve the issue a better way.
do i think it is the end of the world on a short shallow ow training dive to try them out. no, not really.
but the instructor should work with them to sort it out using other solutions.