Not all intervals are the same. You can do an interval that’s 2x69min at 69% FTP, it’s lower intensity…and it’s technically an interval.
Dylan Johnson (and others) advocate for 2-3 HIGH INTENSITY interval sessions a week, which is essentially what TR does. In high volume the sets that are high intensity are vo2 max and the stuff at 105-108% and maybe the over/unders. The others are tempo/sweet spot intervals. They’re still intervals, but they’re not high intensity.
I don’t have experience with every high volume plan, but I haven’t seen one on TR where it has you doing 4+ HIGH INTENSITY interval sessions a week.
Also, TR is built around training indoors and maximizing time. If they make the plans sitting there and spinning at an endurance pace for 2hrs, it’s boringAF…that’s one reason why it’s more centered around sweet spot work. Also because sweet spot work…works, and can be done day after day after day, even if they are all “intervals”