We think he's right but premature.
Mr. Grantham has a habit of being early and because of this his performance record suffers, see:
Feb. 2010
"Grantham’s ‘Horrifically Early’ Calls Challenge GMO"
March 2014
How Good Is Jeremy Grantham's Forecasting Record?
July 2016
Grantham Mayo Van Otterloo's Mean Reversion Strategy Is Tested In Today's Market
One specific call that exemplifies this is a