Ahh, thanks for clarifying! If this is the case, wouldn’t the value that most riders get from assigning zones based on FTP outweigh the benefit of potentially working 10% harder in VO2 max intervals?
And… is the OP actually suggesting that you would stick to TR plans but put in an arbitrary FTP and just go as hard as you can for the duration of each interval?
Right, I think what he’s talking about applies to a very small subset of riders. Even most riders with a Coggan power profile indicating they are a sprinter probably train more aerobically than he’s suggesting. Could those people benefit from going harder in their VO2 intervals? Maybe. But I’m guessing that the 30% range window of that specific power zone probably encapsulates 99% of the people out there without having to artificially manipulate their FTP value to get the desired training stimulus.
In reality, a 5% difference in power in training is not going to result in a tremendous difference in your overall capacity, especially considering the error associated with most power meters and smart trainers anyway. And I’ve never met someone who can peg at exactly 146% of FTP for six minutes without fluctuating by close to 5% anyway. Heck, you can see a 10% difference in power capacity just by going from the hoods to the drops down into TT bars… Again, the concept of “good enough” applies for the vast majority.
Given the widespread misunderstanding of my post, I must take the blame for being a very poor communicator !!
I appreciate folks trying to explain to other folks what I meant, but unfortunately it just muddied the waters because it’s not at all what I meant.
I’ll try one last time to be crystal clear 
My main point was simply that the zone you’re in when performing a structured interval workout is determined primarily by the duration of the work intervals. I think most of us use Coggan’s durations of < 30 seconds for Neuromuscular, 30 seconds to 3 minutes for Anaerobic, 3 minutes to 8 minutes for VO2max and 8+ minutes for Threshold.
Hopefully we all agree that different energy systems (Phosphagen, Anaerobic Glycolysis & Aerobic Glycolysis) are best trained at different durations. So, for example, hitting a 1 minute interval workout hard is going to primarily train your Anaerobic Glycolysis system, etc.
Naturally, this assumes a best effort - barely pushing the pedals around for a 2 minute interval is obviously not a good anaerobic interval!
I’ve used this approach since Mar 2018, and it’s worked extremely well, and I think it’s probably because I’m always pushing myself to the limit - e.g. if I did a 3 x 4 x 1-min. workout at 385 watts, then the next time I’ll do it at 388 watts, for example. I don’t wait for an FTP test to do this, I just make it harder in some way every time if possible. I use the TR Workout Creator a lot to create these custom workouts - I just use two VO2max workouts and three Anaerobic workouts (since I follow a polarized approach, I don’t do sweet spot / threshold work).
I’m not proposing this for most people For one thing, it requires some detailed tracking (I use a spreadsheet), and for convenience, it works best if you use a relatively small set of workout formats as I mention above, but we really don’t need that much variety to stimulate these energy systems - a couple for each energy system is fine.
And as others have noted, it doesn’t work for sub-maximal efforts, so anything below Threshold is a bad fit. Fortunately, Stephen Seiler’s polarized training approach works extremely well with this approach.
If you want to test your FTP frequently, that’s fine, but for me, I just prefer to keep ratcheting up the effort for the various energy systems.
The secondary point that some have fixated on is that this approach also allows for individualization for different types of power profiles, but I agree that point is minor, and most of us are probably in the middle of the bell curve here.
Sorry for all the confusion - for most people, just pick a TR plan and follow it !!
I interpret ‘test more’ as specific threshold tests for various durations of efforts, which would perhaps produce the ‘power profile’ you speak of in Allen and Coggin. It would require a bit more effort to create a power profile to guide your workouts at various intensities.
The process that you describe (of making sure your tailor your efforts based on the length of the interval) isn’t that much different to ‘testing’ 
. In essence, you have created that power profile which you follow each time you work out.
I think your points on the limitations of relying solely on FTP are well made
I agree, particularly in relation to the shorter interval work. In fact the shorter the interval the more there is to gain from this approach e.g. a minute all out is simply that… there is need to worry about FTP or a target power. In fact if looking at reproducability of all anaerobic efforts there is a lot to be said for doing sessions which include repeated all out efforts, it doesn’t matter what the numbers say (they should gradually drop as the set progresses). This also produces a toughened mindset as there is absolutely no hiding place if you are generally ‘all in’. Finally this is just an alternate way of working, which, will work just as well as working to % of FTP and could be used to give variety to training.