I think this really gets to the core of what the OP is asking and I have wondered about myself. Is the principal training benefit from VO2 sessions derived from accumulating time spent with power in the VO2 zone, or from accumulating time spent in a state of maximal oxygen uptake?
Because short 30/30 sessions are great for accumulating time in the VO2 power zone, but my experience is similar to the OPs in that I don’t seem to spend much time in a state of maximal oxygen uptake. Based on HR and breathing rate I.e. My HR often stays mostly below threshold and I’m rarely gasping for breath. Even on workouts that I find hard and struggle to complete or even have to quit or dial down, it’s really only towards the end of the later blocks that my HR and breathing have built up towards what I feel is a state of maximal oxygen uptake. 30 seconds is just so short that by the time my HR and breathing are starting to climb towards threshold I hit the next rest interval and they’re dropping again. Same time accumulated in power zone but via 1 minute instead of 30s intervals typically accumulates more time with HR in zone for me, and 2 and 3 minute intervals better still (though more mentally and physically taxing so there is a trade off).
On the podcast they’ve talked quite a bit about that state of maximal oxygen uptake being what is key for the training adaptation. That just doesn’t chime well with my experience of short shorts. I tend to use them when I just want to touch on VO2 max without too much fatigue e.g. During base or off season (I’m in my 40s and figure it’s good to always do some VO2 as research says use it or lose it). When VO2 sessions are a priority e.g. during the build phase I tend to pick alternate workouts with longer intervals.