High inflation persisted in America in the 1970s. Why wouldn’t it happen again?

Because we have different Federal Reserve policy than we did in the 1970s, for one thing.

The fed in the 70s slowed inflation by raising interest rates to 20%. The current fed will never do that.

Correct. And there is a reason, at 10% interest rate, the federal government is bankrupt.

It could happen again, but equity returns wouldn't be sub-inflation for 10 years, because the real economy isn't shrinking by 4% a year.