...holding that much cash during a sustained bull run...

The most rational portfolio construction method is to be heavily long equities when the upside is large and the downside small, and the reverse. Consequently the most sensible portfolio is one that is very cash heavy (and non volatile) at times of high valuation levels and all-in (and therefore very volatile) at times of low valuation levels. It's not emotionally easy, but it's the most profitable way to go.

So, "holding that much cash during a sustained bull run" is precisely what the smartest portfolio manager would do, particularly during what seems to be the later stages of a bull run. The seem to be complaining about management doing what makes most sense.

Of course, one could try to time the market, thinking "I'll ride it up into overvaluation and then sell before everyone else does". But just imagine trying to sell $100bn of equities when the panic starts and there's a huge crowd between you and the exit...

Jim