I'm choosing those points because I remember hearing from retirees in 2008 that they had followed all of the advice and they are worse off than they were 10+ years ago. I saw too many cases of people being upside-down on their mortgages, while losing their jobs, while losing their retirements. In that situation, it's pretty hard to keep saying "don't worry, it'll come back, just keep dollar cost averaging in". If you were retiring in 2008, you might not be able to keep averaging with the market, even if you had the stomach to do it. Time in the market is still timing the market.
We've only had modern portfolio theory since 1952. In the last few decades, we've done some really experimental monetary policy. I won't be shocked if we experience some event that brings us back to 2008 levels. I also won't be shocked if we see hyperinflation. The one thing I know is that you're always trying to time the market, it's just a question of if you acknowledge it or not.
I think it's a good idea to max out your tax-advantaged retirement plans and dump them in indexes as sort of a safety net because your MPT advice is probably "too big to fail" at this point, but that only accounts for less than 20k/year of investment advice (for most employed people). After that, investing in a residence makes a lot of sense because of the tax advantages. If you happen to be in a situation where you can engineer more tax advantages (like owning a business or moving to a lower-tax state), then definitely do that. Once you've got all that sorted, it's pretty much just gambling.