I will chime in...….
I am no elite athlete, not even close. I have a power meter and its been awesome. Here was my PM training build up to get better.
For the first 3 months I just rode like normal, getting used to the numbers, playing with it you know feeling it out. After 3 months I did a FTP test, the 20 minute one. Then about two weeks later or so I did the full hour version. I used those two tests to get a pretty close FTP I thought.
Then I got a book......yep, used a darn ol book and put together a training plan off that. I would have to go find it, only used it that one season. Now I have a decent regiment and know what the data means and how to use it. Been an awesome tool. I am still no athlete but I am a much stronger rider than I was before a PM. I can't see not having one now. I can climb better now, and know when to go and when to whoa.
It doesn't matter what power meter source you use, an actual PM on the bike or a trainer, as long as you measure with the same PM you will be able to track your progress. That is what's important. So yes, I would redo a FTP and use that only as a measurement. Zwift power measurement is actually pretty close if you compare but they are just a touch elevated I find comparted to my PM.
And the best part IMO they are just so dang cool to measure your watts!