Interesting issue @glendaviesnz! This fix appears to work well for themes where the default styling is for the image block to be centred in the front end view, so it works nicely in TwentyTwentyOne. I noticed in TwentyTwenty, though, the front end styling defaults to the block being rendered left aligned. So with this change applied, in the editor view, resizing the image causes it to appear as though it's centre-aligned, however the front-end view is left aligned.

TwentyTwentyOne editor view	TwentyTwentyOne front end view

TwentyTwenty editor view	TwentyTwenty front end view

I'm not quite sure what the solution is, but it seems that display: table overrides the theme's max-width for the block, so it effectively makes it centre aligned? I had a quick go at seeing if we could pass width to the style of the RichText instead of using the CSS change, but it then meant we lose the real-time updating of the caption position, so probably doesn't really work as an alternative 🤔