An M.2 SSD will definitely outperform an HDD, also in this case.
The scenery data is downloaded from the cloud servers and stored in the rolling cache which acts like a buffer. So the “write” speed is important, which is very fast on M.2. Also, not all the rolling cache data is transferred to RAM, so a fast read speed is important as well.
All in all, a SATA SSD or M.2 SSD is very much recommended, as mechanical drives simply cannot reach the read / write speeds those storage devices offer.