You're making an assumption about the testing that forgets that there are other factors that impact on performance. eg Your 3rd example - watt droppage may not be a result of ineffective workouts, it could be due to a range of other factors (that also impact on HR). YOu are working on the premise that a power meter never lies. Neither does a camera.
And.. you can use a powermeter in a pursuit, so long as you tape your poota bit up, so it isn't going to fall off onto the track, and you smile sweetly at the commissaires.
And how do you test if training workouts are effective -speed/time. If you are going out too hard in a pursuit, you blow up and can't make the time over the distance, if not hard enough, your time is too slow. How to tell if the gym and speed work is working for your sprinter? Take them to DISC and time them.
Some days 180 watts feels fine, other days it feels like hell. That doesn't mean your training isn't working. Powermeters are not the only reliable way to test improvements. And are they a valid test measurement when they are not used in training?
Of course they are a valid test, they tell you, with an appropriately designed test protocol, if the rider has improved their power output or not, and racing is about two things, power and tactics. Yes, there are other reasons for why a rider may drop power, but that does not invalidate the result of a test using a power meter. It *does* tell you that they have dropped power output, which you otherwise would be unlikely to know. I can take a rider to DISC and test them, but they may fluff a line up, take a different line off the bank etc, that test also doesn't tell you if they've changed some aspect of their power curve, and for a pursuit, power analysis will tell you more about how well a rider is pacing themselves than anything else. You can look at small changes in power output that won't show up clearly with a stopwatch (first lap, for example in a pursuit or an ITT, or any road test on the open road or an outdoor velodrome). You can find out a riders strengths quickly and easily with a test.
A power test is easy to do, portable (all I need is my fluid 2 and the wheel, I can do it anywhere, any time), convenient, accurate and very enlightening. I really can't see your objection. It doesn't make any sense. You're rejecting a tool that is known to be accurate and consistent for what reason? Because you're not training with it?