FTP is useful in limited scenarios to most low level racers. Rarely do you go all out alone for an hour.

IMHO, unless you NEED hour power....focus on 8min and less and let “ftp” fall where it may.

If you DO need hour long power.....as much sweet spot as you can handle. Then periodically do a short week with some pursuits or something else more intense.

I did that to try for a 25mi TT personal best, worked well. Broke an hour first try. Bagged a 10mi pr also by a whole 2mph faster than last year.