Current Shiller PE Ratio: 32.32. It was 27 before the crash in 2008. The only time we were higher was in 2000 and that was when companies were selling for essentially infinite multiples. Bitcoin not a factor here, and the private equity markets weren't as bad as they are now.
Mean: 16.69
Median: 15.76
Min: 4.78 (Dec 1920)
Max: 44.19 (Dec 1999)
Busiturtle has some good stuff on interest rates. Which have fueled debt buy backs which keeps the P/E ratio you referenced artificially low. They can use debt to personally enrich management teams that have goals to keep EPS high.
We're the highest we've ever been on the Wilshire 5000 GDP (This is a famous Buffett Indicator). Price of all US stocks is 180% of actual GDP. Never been there in history.
Here's a really interesting analysis comparing today to 2000:
https://twitter.com/Greenbackd/status/1227281799660720129
Plus you have a ton of money just plowing into indexes. The dumbest money there is, which buys and sells underlying equities at any price. This is the thing creating the massive bubble. Stocks that have $5 Million in daily volume outside the index have $100 Billion daily volume while participating in the index.
Brave new world. Prospects for great returns are low and probability of huge pullbacks are high in the next few years. People should get ready versus trying to participate in any last stretch run-up. Then again, you're right, no one knows when, and they can just commit to buying into the market as it freaks out and holding as it melts up again.