If you are doing a FTP test, then you must have a PM. My power zones and HR zones don't match at all. They aren't supposed too IMO. I'm not to worried about the ambiguity between them. I'm just riding for overall heath and cardiovascular fitness too. So I don't even use a set training program. I just go for a ride and know there needs to be some easy elements and hard elements mixed in.
Cycling IMO, doesn't do much for for some of the other fitness needs we old people have. And it's notable to me that cycling and walking don't work all the same muscles and those they do aren't worked the same way. So walking is important too. So it's probably important to do some other things too that involve more strength training just to maintain the muscle mass. Particularly the upper body since cycling, at least for me, does nothing for my upper body... other than lungs and heart.