I think Dorian made a large emotional investment into each workout and each set. That's why he felt he trained harder than anyone else. If you just look at his workout from the outside it doesn't look like anything special.
Those that love "hard training" know that there's a difference between going into the gym with a laid back attitude and doing sets to failure and beyond vs. thinking of a certain set for a week and going in all hyped up and desperate to hit a PR. The second can really drain you whereas the first might look like more work.
Another way to illustrate this is by way of powerlifting competitions. It's a maximum of 9 single lifts. Not a ton of work, not many seconds of effort, but the emotional investment can be huge, and it might take months to recover from fully.
If you look at Milos' giant sets, they are very laid back in a way, simply because you can't, by necessity, go 100% every inch of every movement. So the movements get a little sloppy and there is little grinding lifts and hard failure points, and so on. If you did giant sets like Dorian did his sets no one would survive it. Maybe one workout but not as a constant way of training.
