I love my way is better than your way views. I personally took a hybrid approach where I maxed out retirement accounts, had meaningful emergency fund, made extra payments to the mortgage, had a HELOC, and invested additional amounts along the way - and it worked for me but might not for others, I liked that my stash was growing, debt was reducing, and I had funds to whether storms.
There is no right or wrong answer because the answer is based on the individuals personal risk tolerance - which may or may not be consistent with common views on the subject. The historical math suggests that one will do better by investing vs. paying off the mortgage, but two things that are typically ignored are the difference isn't always that great at the end, people don't generally adjust or know how to quantify for the additional risk (ie risk adjusted return). Plus the mortgage deduction is largely a myth for most people as the standard deduction (especially for families) typically exceeds the mortgage and other deductions or AMT starts coming into play to wipe out some of the benefits.
Anyway, take a $200,000 mortgage at 3.5% rate for 15 years and compare out comes for extra $1000/months at end of 15 years.
Inv Return Invest Payoff Mort then Inv Diff
7% $317,000 $262,000 $55,000
5% $267,000 $243,000 $24,000
Leverage is what makes it better, and leverage adds risk. Plus paying down the mortgage is a guaranteed (risk-free) return. So by investing with leverage you would be compounding the risk, which is fine but that's how the decision should be made because the 5-7% or even higher are not guaranteed. Leveraged returns just as easily go the other way too.
S&P 500 has a current PE of 22 and a forward PE of 16, said otherwise expected current return is 4.5% or 6.3% the difference being attributed to inflation/operating leverage/efficiencies. Yield to maturity on Vanguards BND is 2.23%. With a 80/20 split that would result in an expected return of 5.49% using the forward PE - increase the bonds it goes down, go all equities and it goes up the range is 2.23% to 6.3%.
For me, to realize an expected return of $24-30k in total over 15 years with the added leverage and market risk I don't think is worth it. That is just this point in time though when comparing expected returns to the 3.5% mortgage rate.