You are correct here, however, the large file + CUE was only required in the past when players could not play a sample accurate gapless stream. This is no longer a real problem with modern playback engines designed to handle this properly.
FLAC file lengths can be CD sector accurate (no padding), and Roon can play sample accurate gaplessly.
In Roon, whether you stream TIDAL or play FLACs (or any other file format that does not pad), the playback is gapless as long as the format of the audio is the same. It’s as good as a CUE file. In some ways, even better, since you can gaplessly play between non-contiguous tracks (like Nonagon Infinity, which is gapless from last track to first track.)
To directly answer your question:
We feel that CUE files are an obsolete piece of technology, and that there are better more flexible ways to store your content with no loss in quality, assuming the software handles the playback properly. We may add support for CUE files in the future, as a way to support Roon members that have data in this legacy format, but if we do, it would result in reduced functionality as the format is not as flexible as our feature set requires.