Interesting discussion - I'm pretty confident that my FTP (obtained by TrainerRoad ramp test using a smart trainer) is too high, as I know I'm not that strong a rider on the road. I'm either very good at doing the ramp test (e.g. I'm quite fit from a cardio perspective outside of cycling), my trainer is over reporting power (I have no other power data source to calibrate it against), or the ramp test results are flawed.
That said, none of the above really matters to my training, what's key is consistency / repeatability - I need to be able to train in the right zones, and if my FTP is reported at x% too high, then the intervals I'm doing should be reported at x% too high as well, and therefore be about right. If I keep everything consistent between testing and training, I can measure improvement in power / fitness over time, even if the actual figures themselves are detached from reality.