Mathematically, there is never a tipping point where paying off debt at a lower rate than what you can (expect to) earn investing the money will make you richer. That is just maths.

In OP's case, he is deciding wether to liquidate all his accumulated investments so far to pay off the outstanding debt on the house and restart from scratch, or carry on paying mortgage and let his investments continue to grow.

Assuming 7% investment return:

In scenario A, if he stays invested, his 140k pot grows to 620k after 22 years even without any further contributions, and he makes the final mortgage payoff, so he is left with 620k and a paid off home.

In scenario B, if he liquidates his investments and pays off the mortgage, he restarts from zero but now invests 9.7k/yr cashflow he's freed up. 9.7k per per invested over 22 years gives you a final nestegg of 420k and a paid off home.

Scenario A wins

It doesn't matter what rate of return you use, so long as the growth in investing is greater than the interest rate you are paying on the debt (net of taxes, of course) then you come out ahead by investing, all other things being equal.

*Behaviourally* there can be case made for choosing to prioritize the mortgage, as people tend to be adverse to debt and prefer the certainty of debt repayment to the uncertainty of investing returns.