Anyone holding a high percent of cash believes better opportunities are ahead. Isn't that market timing? How has that worked out to date?

That's not really market timing, that's just market pricing. Little more than "don't buy stuff without a margin of safety", which doesn't seem like a bad idea, and isn't particularly difficult.

The only bit that is "timing adjacent" is the belief that a decent opportunity will come along soon enough that the wait will have been worthwhile. Historically that has been true, but the future could be slightly different. Someone could perhaps make the case that deep value investing doesn't work as well as it used to as the time between bouts of rational pricing are more widely spaced of late, making the annualized return boost lower from any given level of discount achieved at purchase time.

As for how well it has worked to date, well, about best investing result in all history?

Jim