What a great topic, happy to see a serious discussion.
Have been thinking about the ramp-test for quite a while, and one wonders if we still don’t have anything better after >25 years? Francesco Conconi used the same test in the 80s to help Moser determine (and improve) his anaerobic threshold for the world hour record attempt (oh yeah, and some blood doping as well, different topic). Conconi used the deflection point of heart rate vs power to determine threshold, and the .75 rule from TR is basically a simplification of the original Conconi test.
TR is likely hesitant to use HR as it is affected by hydration, fatigue, temperature, altitude, etc. But as we mere amateurs are unlikely to measure oxygen intake or blood lactate, it still might be one of the only biomarkers that is available.
Based on the many comments on the forum the ramp-test is a serious weak point in the TR approach. Using a combination of the power curve (like Sufferfest), HR and workout compliance as inputs to set training intensity seems to be the way to go. But certainly not trivial, as transparency would be hard to provide and TR might also have to build ‘all out’ efforts into their plans. And that would likely lead to many complaints as well, as many users seem to enjoy the ‘follow the power-line’ approach.