I have similar sentiments re FTP setting to be too high but it can also be a function of workout order or fatigue in the legs. I tend to be in good shape on Tuesdays which I would aim to do my hardest workout for the week. So lately in the program the first two workouts of the week were VO2 and threshold which are done Tuesday and Thursday. Threshold work felt hard and was challenging to get through that last interval of different workouts. I switched around my days to move my threshold workout to be the first workout of the week and VO2 later. What I noticed was my threshold workouts were going better. I now felt it was easier to push the threshold work on Tuesdays as the RPE just became better. Both workouts have their challenges but having fresher legs made the threshold feel a lot better.
From my personal perspective breathing hard isnt as challenging as doing harder muscular endurance work but we all have our own challenges.