If you don’t care much that you’re out there in the virtual world with others suffering together, then there’s not a huge value to seeing other riders. As for the graphics, I suppose seeing the 3d markers on the map showing start/ends of intervals serves a purpose for some, while others might be fine just seeing a clock count down. It’s up to you.
Often when users are doing their FTP tests they’ll end up getting “ride ons” from other users to help encourage them during their time of pain, and to me that encouragement sounds like it’d be valuable to almost anyone.