Even more the case to choose the option which allows you to FIRE quicker. :)
The math wins argument is too simplistic in nature and ignores certain aspects:
1. It ignores relative risk in the equation - Paying off a mortgage is a guaranteed risk free return. Not paying it off and investing will likely yield a higher return over time but it is not guaranteed.
2. Its based on historical averages - you don't know if a you are investng right before a high returning market or an imploding market. Sort of a market timing element to this. But the your view in hindsight will be completely different depending on the outcome.
3. Different people also have diferent risk tolerances - someone inclined to pay off the mortage would also be likely to have a more conservative asset allocation and therefore the return differences would be less.
4. It ignores duration - average time in a home is 5-7 years, due to different stages of life, job changes, simple desire to change, etc. So more likely than not your 30 year mortgage at 3% will not see it through to the end.
5. It ignores taxes - there are still taxes on capital gains, dividends and interest and mortgage deductibility isn't as much of a benefit as most people think given the standard deduction levels.
When the 30 year was at 3% - it made more sense to invest especially with dividend yields of 2%. But now as the the 30 year rate is approaching 4.5% I don't think it is so clear given that a balanced portfolio would return 6-7% then that may not warrant the increased volatility and risk but it still is a better return.
You do give up liquidity and have concentration in a single asset - these are the big risk items that people don't consider who are on the pay off the mortgage side - I wouldn't advise anyone to pay off the mortgage if that is all you have (i.e. if you have a $200k house and no other assets then taking on too much risk but if you have a $200k house paid off with $1mil in investments you still have a concentration but ample liquidity to offset it. Also the return differential is really only made apparent if you have the choice today to pay OFF the mortgage or invest the whole amount, it is not as great if the choice is between making extra payments to the mortgage or invest it.