That isn't true when we consider interest rates. The 30 year bond is at a record 1.8% low -- even below the target inflation rate. That is crazy.
People tend to view stock valuations against historical norms for P/E ratios, but we are far from historical norms with interest rates. Further, public debt is such that interest rates cannot be raised appreciably. It will get worse as the government prints more to prop up the economy.
We might have a major correction with this pandemic, but when that plays out I would expect to be at new highs again provided we don't panic and turn to a socialist government in the forthcoming elections. That would be the real stock crusher longer term.
Obviously you are ignoring about 250 indicators. Nice overworked theory that failed miserably in the 1930's.