My take is that markets may stay irrational much longer than investors can remain solvent. In other words, you will go broke if you short the markets too much in the long run, if you bet on a recession or a collapse of anything.
Markets are about supply and demand. If central banks are willing to buy and do "whatever it takes", it is not smart to fight them, no matter how much you think the markets are overvalued or in a bubble.
BUT, there are plenty of overvalued stocks, especially in this frothy market. So it is very easy (and prudent I would say) to have a more or less market neutral portfolio at the moment in stocks (long-short equity strategy).
Plus a truly diversified portfolio that includes many asset classes (some real estate, some U.S. Treasuries, some gold and various other asset classes and diversified strategies) goes a long way in the long run.