This is getting tiring, even for me
There is just no evidence I've seen that shows that a low interest rate mortgage is a hindrance to retirement. If you don't care to have a mortgage, fine. But to call it good/bad advice is simply not borne out by the facts. To consider it to be 'important' to retirement, well, it just ain't so - either way.
Someone with $750,000 portfolio and a low interest $100,000 mortgage is NOT going to be at any huge disadvantage (or huge advantage) to the same person who paid off the mortgage, and now has a $650,000 portfolio.
But they are very likely to come out somewhat ahead over 30 years, by holding a low interest rate mortgage.
I did a FIRECALC run using $35,000 spend on $1,000,000 (3.5% WR) for easy math - this just gets you to 100% success for 30 years, with all other defaults. You can see the very bottom line, and FIRECALC reports you end with $87,138 remaining. This worked out to a cumulative 0.8% real return for the single very worst period
out of the 111 tested (the second worst appears to have ~ double the remaining balance, taking the real return to ~ 1.1%).
, only goes from 1946 to 2005, but it shows inflation over any of those 30 year periods to range from 3.43% to 5.44%. So a 3.5% mortgage sounds like it would have been a winner at practically any time in the past, even if low nominal portfolio returns coincided with a period of low inflation. Surely, it can't be that risky as to derail a retirement? I fail to see how. Can you explain?
Again, someone may choose not to have a mortgage, but to 'advise' others that it is important to FIRE? I don't get it.