Admittedly it's an extrapolation, and doing a 1 hour TT is the best measure of your true 1 hour power.

For me at least the CTS extrapolation is pretty accurate. I've had my LT threshold measured in a lab, and then done a CTS field test a couple of days later, and came to the same numbers for my LTHR, and FTP.

And my 1 hour TT times are consistent with what you would project based on my FTP as calculated by the CTS method.

In my experience the CTS test is certainly adequate to set training zones, and to measure relative progess, and a lot more practical than doing 1 hour TT efforts repeatedly.