You only have to look at the size of the “Ramp Test Tips & Tricks” thread to see how important the number spat out at the end of the ramp test is to people 
The problems you mention are why it’d be a big improvement for the TR software to make adjustments to FTP based on RPE throughout the plan.
There’s so much of an obsession with AI and big data that guiding workout intensity using RPE is usually overlooked.