Isn't the issue that the "rules " are set so as to set a certain standard ?
I would be quite happy if formal nights became "dress to impress " nights. DJ or kilt, if you wish, but a decent jacket and shirt and chinos if you wish (talking as a chap, obvs) would be perfectly OK.
However, once you go down that route, the flood gates open, in as much as a clean tee shirt and decent jeans can be seen, by some, as obeying the dress code. Good luck to the Maitre'D deciding what is acceptable and what is not.
I have no answer !
Personally, on a cruise from Southampton, I will pack a DJ (two in fact!), but on a fly cruise, a jacket and chinos, with tie, will suffice.
Just to add, in the three or four years prior to stopping working, I gave up wearing a suit. Just couldn't see the point. So, decent jacket and tie and smart trousers. None of my customers (JS, M&S, Tesco etc) seemed to care, and my overseas customers cared even less !