Remember, the loan is locked in. Everything around you may be a high rate environment, but your loan is still 3.5% when regular bank savings account would be paying, say 7%.
So, if you bought shares of an Emerging Markets ETF [1] with the money that you would have otherwise paid for accelerated mortgage payments. Today these shares are paying you around 3.5% in dividends alone.
Fast forward ten years to a high rate environment, and ten years of buying ETF shares and reinvesting dividends, I'm assuming that the dollar amount of your shares would be higher than the amount of debt you would have otherwise paid off already.
That's why no other country on Earth that I know of has 30-year fixed mortgages. They are essentially a government subsidy to homeowners via Fannie/Freddie.