Welcome to EF xander! You certainly can't argue with Mike Rashid's results. I think as long as your diet/supplements and sleep are good, you can train this intense and get excellent results.
I mean, there's a certain point where you can overtrain to the point of detriment, especially if you're not doing steroids or SARMs. But I think some people use overtraining as the boogeyman to convince them that it's alright to skip a day in the gym and/or avoid pushing out those last 1-2 difficult reps.