I thought so! Apart from the following point of yours perhaps:
Firstly, I think this type of work in general is much needed as a supportive, indirect rather than direct training means (e.g., some of the physiological adaptations were previously mentioned and are well known).
Secondly, for a 400 m runner who relies more on his speed, I would prefer a tempo-like training means, as prescribed by Charlie and perhaps irrespectively of the identification of a threshold intensity -if the last drill is the same time-wise, if not (potentially) a bit faster vs. the first one (a tempo ‘criterion’), I am pretty sure lactate levels will be steady anyway, despite the work being performed at a speed higher vs. the threshold. For a 400 m runner who relies more on his endurance I would likely be interested in knowing this threshold intensity and even more so if the athlete himself is convinced (e.g., due to his training background) that continuous runs are a must for him. Then yes, I would incorporate both training methods to please both sides at minimum risk/conflict. In the latter case though and exactly because of this training background I suspect the intensities of the two methods will be quite close to each other…
Yes, of course!
The fact that people have tried to define an intensity with false/inaccurate terms and/or methods doesn’t mean that the “phenomenon” does not exist!
Not to mention the research that shows that what it really matters is the average workload irrespectively of how that is achieved (e.g., via intervals around -below/above- the threshold). The question is whether this is an appropriate area to be in for those athletes that it represents a middle ground…
In any case, it’s nice and productive to be accurate and discuss such issues, but I very much doubt any of us would hurt a 400 m runner with any sub-VO2max (if we need to define it) conditioning work. As James said, I think we are more in agreement than not…