Your point about valuation being a bad timing metric is correct. A lot of people see high multiples and think that a correction is a foregone conclusion.
What they’re missing is that the market is both more efficient today and more forward looking than it used to be. Sometimes when the multiples appear stretched it’s because the valuation is based on profitability that is expected to be achieved in coming years. Multiples can go back down either by price decreases or profitability increases.
Sometimes the market can correct just by sitting trading for a bit while underlying growth reduces the multiples.