I could see an argument made that the placement of the subtitles in an arrangement for ease of reading, without blocking key visual information, placed such that a viewer can identify which subtitle is spoken by which character, timed such that jokes are not given away prematurely, has a creative aspect in order to make sure that all such constraints are met when creating subtitles.

It isn't a good argument, but I could see it being made.

Subtitles are literally just the scripted dialogue in textual form, so the copyright would belong to the studio (having purchased the script from the screenwriter).

Translated subtitles would be copyrighted by the translator under a derivative license from the studio owning the film.

Subtitles of the type you suggest don't currently exist as standalone products; the level of detail and information you are describing would require the subtitles to be part of the film itself (see e.g., Atomic Blonde or John Wick for good examples).

ASS subtitle format is rich enough to encapsulate this. You see it in anime subs. They're distributed with the product, but it's a separate stream in the MKV.

Well, yeah, the script of the movie is copyrighted.

The copyright of the movie script & audio track extends to the subtitles. It's not an independent work of art, but it's part of one - and the copyright holder certainly can licence you only part of their work or only certain forms of their work, and they've chosen to grant you one transformation and not another.