I agree. It’s absolutely a useful tool and I also agree with you and @trpnhntr that it doesn’t really need a precise definition to have that utility.
However over the time I’ve used a PM it’s been variously described as
The power you can hold for exactly an hour
The power you can hold in a quasi steady state for approximately an hour
“Some people can only hold their FTP for 40 mins” (with the advent of WKO4?)
Yours was simply the first time I’ve seen somebody reference sub 30 minutes. What I do smile at given this disparity in definition is seeing people worry over whether their FTP is 240 or 250 when we can’t even decide over which duration they should be holding that effort.
Yup. Although other points on the Power Duration curve may have as much or potentially more significance depending on your goals.