Well training for that is way more time and facility intensive than most folks can manage.

So the takeaway becomes "oh, if I move around in a pool for 20 minutes every couple of weeks that should be really good at weight management".

Yes swimming is nicely low impact so you can more credibly stand hours a day of that much intense activity and between the activity itself and the energy hungry musculature you get it can make a difference, but that is way way beyond realistic for all but a tiny bit of the population.

Realistically, realistic exercise is good for various things, like joint health (when done correctly), cardiovascular health, insulin response, and tons of other stuff. However it will not manage weight that well nor stave off all the associated health risks.