Oh, I forgot to refresh the page - the toolbar shows up now.
We use displayedData in Legacy Table to build a HTML table off the data after filter, that we open in browser (as copytoclipboard does not support HTML mime-type - see here) and copy/paste in Excel. HTML allows us to format the data e.g. colorize, hyperlinks (with title), ... XL and GSheets parse html just fine.
Another use case is aggregate numbers - we have a text box which sums up the filtered numbers in a given column. As the filter changes, so does the sum. How can this be done in New Table if displayedData is not available ?
Interestingly the Download button in the New Table exports the data filtered but that array is not exposed in any property.