Another view:

Yes, it seems that US large caps are more richly valued than has been historically typical, and that effect extends to the cap weight indexes they dominate.
And yes, the valuation gap between those biggies and the non-US and/or smaller cap equities seems to be bigger than what's historically typical.
Those conclusions can be shown in a number of ways, and are generally pretty extreme these days.

However, it's a big leap from those pretty solid observations to deciding that moving money to a specific different corner of the market will increase your returns. The world is a very difficult place to predict, and even when it seems easy the timing can be impossibly hard.

The way I address that impossibly hard problem is to dodge it. I invest almost exclusively in individual equities that I don't deem to be overvalued, so in theory (!) the broad market valuation level doesn't matter a whole lot. I pick the best I can without much regard to the company size, and it tends to bounce all the way back after any price swoon. If I can't find enough things that seem to be reasonably valued, the cash allocation rises. But it's a whole lot of work to pick a sensible stock astutely, and heaven knows most people get that evaluation wrong a lot of the time (including me), so maybe that's not a good solution either.

Jim