breasts do not work that way, dude
I would accept your refutation, if that dance had more actual bounce to it. I'm a big titted lass myself and I can tell you that those dance moves were all performed verrrrrry carefully and are bounce-minimal. There is lots of "ooh look at my arms and legs moving, my arms and legs moving very much" but all the torso movement is slow and balanced with the exception of one or two fast-looking moments. We also have no idea how many outtakes there were on this - the amount this scene is cut with different angles and camera views, there could have been 50 takes of this scene and we would never know.
I can't see any bodysuit, and I will happily concede that very high quality adhesives could make a costume like the full covering bellydance bra stay put, but I can tell you why the superhero costume would not work for fighting, above and beyond the argument for "not staying on". Fighting is a high impact activity - that dance is decidedly low impact.
High impact issues;
Breasts are fluid. Mine try to fight their way out of a full coverage bra if I do anything more active than walking - in a plunge bra I generally have to shift things back into place every 30 minutes or so to avoid accidental nipple exposure.
Breasts are heavy and hang in skin. I wear specially designed big-boob supporting bras most of the time and special sports bras for any kind of activity, and even then running is painful. I mean really painful. I have damaged my chest skin before trying to run for a bus in an insufficiently supportive bra. Running/jumping/anything aerobic is also hard because, if my breasts bounce too much, it interferes with breathing by tugging on the ribs and makes me run out of breath faster.
I also, despite training with weights and practicing pilates, suffer from frequent and severe back and neck pain despite my good and supportive bra-wear. Codeine is a regular friend of mine. My lower back has a permanent deep arch in it from trying to stand in a way that balances my chest, I get frequent pressure headaches stemming from damaged neck and shoulder muscles and sometimes my shoulderblades lock up so bad I need massage therapy to regain full use of my arms.
If I tried to fight... ONCE... in a costume like that I would need probably a fortnight or so of physical therapy to be able to do normal things. And no, physical training will not fix this, not even physical training to a high level; maybe if I was an expert martial artist in addition to my other exercise practices I would need less physical therapy, but no way would I be absolutely fine the morning after a fight in that costume. There is a muscle wall behind the breasts that can be worked but... again... that in itself does not prevent the weight of large breasts from doing damage like I have mentioned.
I know there are arguments that alien women might not have the same physiology... despite somehow having the same body shape as a human woman... but I find it convenient how alien physiology always seems to affect breasts in just the right way to allow for fanservice.
Interesting argument though, and nice to see video evidence offered for a change.