Agree! For fysiological adaptations I would aim for accumalated time in high heart rate(>90%hr max). Maybe start interval at high % FTP to ramp oxygen demand and reducing power output to grind 6-8min. No ERG mode, no pwr target, focus on high hr and heavy burn. Rest between intervals could be extended just to be able to reach and maintain that high hr.
I tried to get that kind of workout done with TR Workout creator, but there seems to be problem refreshing and uploading workouts.