And I agree with the most important point being advisors' ability to coach and manage their client's expectations. I really believe that is the future of the financial services industry will be all about relationships and behavioral coaching.
And, yes a 60/40 will have lower expected returns than a 100% equity portfolio. On paper, 100% equity is the way to go for folks who aren’t about to retire.
The behavioral risk is where the 60/40 (or some allocation to bonds) can save people. 100% equity is only the better choice if people can avoid the temptation to sell when things get scary.
If we are dealing with a completely rational investor, the behavioral risk is low and 100% equity likely makes sense.
I work under the assumption that many of my readers don’t fit that description which is not a knock on them, we are only human. so to reduce the behavioral risk of selling during times of high volatility they might consider some allocation to bonds (to reduce volatility) or they might want to work with an advisor who can coach/guide equity investors through periods of high volatility.