Is Critical Power a Good Metric to Measure FTP?

With critical power it could be like all right we need a three-minute test and a 12-minute test okay what is all right so now I measure somebody's critical power at like let's say 420 watts or something like that great but what if their actual functional threshold power is like 380. You can do maybe like three by ten and they're wrecked by the end of it maybe that's not a good way to measure it. For instance one of my pro athletes his his power over threshold has not changed drastically from last year like his five minutes gone up a lot 20 minutes gone up  a lot. If I give him some proper critical power test durations while he's fresh I