firstly, just to make sure folks are clear FTP isn't strictly 1hr power, if you search around you'll find Dr. Coggan has refuted this many times, it's really a long sustained duration, usually around 40mins or more. My FTP is currently 290 and I know for a fact I couldn't do that for an hour at this point, but using it as the basis for intervals like sweet spot works well for me.
A few years ago when I just had the fluid trainer and my powertap wheel, I would do a lot of races and it was a matter of being able to sustain FTP for longer and longer durations. By one point I was averaging FTP for 70mins and really close to it for 90mins with no breaks. It takes time to be able to develop that ability. But if you're doing interval work, go with what you got on the FTP test. Try to do some of the workouts (there's a 2x15 at FTP workout in zwift that's decent). I personally use trainerroad (and just use zwift for visual distraction) because I find more success in doing structured intervals vs group rides, but I think if you just keep challenging yourself to hang with groups you'll start to get stronger as well.