As mentioned, we’re getting into discussions that have been had quite a few times across various threads on here recently. Maybe we need a new thread to consolidate, given it’s coming up quite regularly? I’ve certainly stated before that simply picking “80% of my FTP” the week of a 70.3, having done a ramp test on the Monday is a pretty stupid way to approach pacing a HIM bike leg. But that doesnt mean the ramp test itself is meaningless.
How you pace a 70.3 is dependent on your sustainable 2-2.5 hour power, also factoring in your ability to run off that effort. Whilst your conceptual FTP might weigh into that pacing decision, it’s far from the only piece to the puzzle. As GB says for running, some people are great at short distances but it doesnt translate to longer stuff. It’s just like those conceptual best tables for running … doing a 16min 5k might suggest you should be capable of doing a 2:40 marathon, but just because you are trained for a 16 min 5k does not in any way mean you are trained for a 2:40 marathon.
But it does offer an insight into likely capabilities. Matt might not be able to do 60mins at the FTP zwift / training peaks suggests right now, but if he adapted his training to focus on an hour attempt, then the numbers he has hit over 20mins would, for the average person, mean he could probably get quite close to those numbers when suitably trained.
ETA - the structure of trainerroad plans are almost a prime example of “growing into your FTP”. If FTP was simply what you could hold for 60mins, then you should be able to do a 50min effort at sweetspot quite comfortably a couple of days after a ramp test. But most people would accept that’s not realistic. Instead, the trainerroad plans slowly get you more and more comfortable with prolonged durations above, at or just below your tested threshold. Intervals generally increase in length, or rest reduces. Over time, that tested FTP that has demonstrated your likely capabilities becomes more and more sustainable for longer and longer durations. Until you hit a point where, in all likelihood if you fully tapered, you could exceed that power duration for well over 60mins, at which point you test again, get a higher number, and repeat the process.
ETA2 - on the assessing your FTP accurately, I’ve always equated it to the heisenberg uncertainty principle. The more accurately you try and test your FTP by properly tapering and doing it as roughly an hour effort, the more you’ve actually undermined your training and performance gains in order to undertake that kind of test (you’ll have slightly detrained during taper, etc). Hence the various approximation methodologies, which, if you know their caveats, are more than good enough. The way trainerroad structure their training plans after a ramp test for example, demonstrates they are fully aware most people probably can’t go and bosh out an hour at that power level a few days later.