Interesting video. I can see her points for folks who are "casual" exercisers possibly needing more HIIT type training to improve VO2. As you become less casual, it appears less likely you'll be a "non-responder". She was talking ~ 2.5 hours of Zone 2 stuff and the study reflected that by simply increasing that frequency/duration pretty much nullified the "non-responder" designation for increasing VO2.
Personally am a big advocate of Zone 2 training, but I also have the luxury of being fully retired. On a normal week (no big trips, non-hunting season) I'm getting about 10 hours of hiking/week. Just by casual observation, I'm very close to the 80:20 rule she brings up. The areas I hike locally have a lot of elevation gain/loss, so pretty much every hike I'm getting into at least some Zone 3 and sometime Zone 4 stuff climbing.
My observations are that a lot of hunters want a quick fix- the 6 week "Monster Mulie" routine, the 8 week "Big Bull" routine, etc. The vast majority of those programs are HIIT training (w/ some strength training as well). While these type of programs will make you fitter than when you started you're missing a huge chunk of what is needed on backpacking hunts (this is the backpacking forum! :D)- endurance. Endurance is gained slowly, measured in years, not weeks. Zone 2 training is proven out and the most elite endurance athletes subscribe to this.
Do you need Zone 3 & 4 training mixed in with your Zone 2 stuff- absolutely; should it be 50:50- if you're only able to exercise a short amount of time/week, possibly that is accurate????
Nothing to do w/ the video, but obviously adding a good strength training component to any regime is going to pay dividends as well.