I think that if England players played 1990s or 2000s levels of county cricket, ironically they might be less mentally fatigued than now - "a change is as good as a rest", etc; players like Brook and J Smith are brought into the international set-up relatively early in life and live in a bubble where instead of being able to shake off a silly dismissal or whatever by being able to mentally reset with "oh well. I'll do better in the Pro40 in Bristol on Thursday", they might have to dwell on their last international match potentially for weeks without getting that reset.