From what I was told on my recent trip to French Polynesia, there are really only three spots where swimming with humpbacks is advertised - Western Australia, Tonga, and Moorea. The first being cooler water and less stellar viz, the second having the best whale action but being the hardest to get to, and the third is accessible and has good conditions but fewer whales and management of tours seems to be on the "honor system" only with no cap on the number of operators.
The operator I went with on Moorea was considering pulling out of whale tours to focus on sharks as the number of boats has gone up exponentially in the past few years, jumping by over 50% in 2019 alone to 33 boats. We got some good encounters, but some of our best happened when our strategy of "get out early and stay out past lunch" paid off and it was just 3-6 of us in the water plus a guide.