I’m actually going to take issue with the very basis of your line of inquiry. I’m not sure we’re actually interested in the “absolute” FTP physiologic value that the ramp test estimates. The purpose of the ramp test cannot and will never be to come close to an accurate representation of this biological number. It’s a training tool, a number upon which you can pin your training sessions. While I completely agree with your assessment of the sources of error, I’m not sure they’re “distortions” in the way you’re mentioning, because literally any strenuous physiologic test will have anxiety, fueling, etc. as possible sources of variance that aren’t an absolute change in the physiologic value of the FTP.
The ramp test probably does depend on more than just “maximum aerobic power,” it’s probably some combo of that and VO2 and lactate processing etc. etc. Regardless, it still generates a number that allows most people to complete workouts at the maximum level of difficulty without burning up. This number might be close to some actual physiologic value or not, but the fact of the matter is it generally seems to work. I think the nature of the questions you’re asking are so individual, that there is unlikely to be an underlying generalizable fact beneath them. Even if there were, the easiest way to address this value is to just tell everyone to troubleshoot it themselves the way they already are: do everything as close to the same every time as possible, and if you feel the number is off, do a workout you’re familiar with and see if the level of effort matches your expectations.
I’m not quite sure how a 20-30 minute traditional FTP test addresses any of the sources of error you bring up, and it also introduces a new, even more difficult to contend with source: you have to guess what you think your new FTP is at the beginning of the test and hold on for dear life. I’m not disputing any of the sources of error you bring up, just disputing how “interesting” these things are from a scientific standpoint in the context of the ramp test. It’s such a multi-variate, complex process, I’m not convinced of your ability to quantify or model these sources of error in any meaningful way that couldn’t be more effectively and easily dealt with by individuals experimenting with their own physiology and seeing what works.
Just my two cents, thanks for the interesting thoughts!