And the herd is voting on this one, and it repeatedly is getting booed off the stage.
The Victorians went to one extreme, and saggers have gone to the other. Neither is to be admired or emulated.
As to the costume epithet, agreed. Almost all manner of public attire could be so termed. When one spends time trying to look ghetto, or preppy, or grunge, or Emo, or any of a hundred looks, one is certainly assuming a costume for a certain audience. The Victorians weren't unique in that regard.
And yes, the beach and the pool have most certainly become more sexualized in the 20th and 21s centuries. Ironically, men's swimsuits did a 180 in the U.S. after trying briefly to follow S. America, Europe, and Australia, but probably 95% of bathing suit sales for men seem to be in the trunks vs. any Speedo or even squarecuts. Yes, there are some areas that see some of the small one, but they are very few statistically.
It would be ludicrous to look as the near-naked fashions of today's smaller swimsuits and presume there is anything but sexualization going on, as all the marketing is exclusively so aimed. But, one chooses where to swim, and with what type of atmosphere.
The streets, stores, and schools of the public areas are not such dedicated spaces to that sort of display. People find various degrees of undress in dance clubs too, but a different standard should and does prevail at the grocery store.