Interesting. Grantham's been a "permabear" for most of my investing lifetime, at least toward the megacap indexes. No idea if his contrarian "anti-trend" funds have done well over the years.

Most of his funds haven't been stellar, as I recall. Conservatism will do that. I believe they has a newish non-US small cap fund that's off to a good start.

But it's not quite fair to label him a permabear.
March 2009 bullish note gmo.com - Reinvesting when terrified viewpoints
Jan 2018 bullish note gmo.com - Bracing yourself for a possible near term melt up viewpoints
That one was not particularly fantastic--the market went up but did not soar--but it's not a bear call.
He even made a claim that "this time is decently different" in 2017, noting that profit margins since 1997 had been 30% higher than the average of the prior 70 years.
And of course, he's been at it a long time...he was very bullish through most of the 1980s and 1990s.

A bigger question is whether it's possible to be an insightful commentator on finance and economics without having a history as a market-beating money manager. I think so. Having dabbled at both, I have an appreciation of the very different skills involved.

Jim