The market isn't that overvalued. Maybe not overvalued at all. It's just up a lot since it got clobbered in 2008. It's actually reaching pretty normal historical levels. the djia is not a very good indicator; it's a far too arbitrary selection of companies and far too few of them.
I disagree with "immune". A bomb goes off in the street, the market crashes, why? THey aren't correlated, the bomb doesn't affect mREITs, doesn't affect Ford's ability to produce cars, etc.... Yet the market tanks.
People are irrational. Many studies point to 80% of stocks correlating almost perfectly to the overall market. 20% correlate to a lesser degree.
Market up 1%? All things constant, AGNC will be up .5% to 1% as well. Corrections follow.