As mentioned I am not concerned with the ups and downs of the market. I feel like I have at least 30 years to invest and a downturn stinks but I am concerned about my total investment decades down the road. Side note, I don't plan on early retirement, but if you do this fund is excellent for taxable accounts due to low turnover. What do you think? Is this a crazy, too simple to be true, portfolio?
This has been answered correctly by many already, but I'll try to offer a different perspective.
First, we have to agree on a foundation belief that a rational investor is seeking the
highest risk adjusted return, not the highest return. What this means is that a rational investor should be willing to trade a certain amount of return in exchange for a certain amount of risk, and vice versa... and this goes in both directions for more/less return and more/less risk.
I got rid of the idea of international funds due to the fact that roughly 50% of the revenue and 50% of the profits of the companies in the S&P 500 come from outside the US.
This is a common misconception. Remember, as a rational investor, you seek the highest risk adjusted return. Simply obtaining sales from a certain geography doesn't make a difference. Let's make a fake example. Say you have two companies in the entire world. Ford makes and sells cars in the USA, and is a "US equity". Toyota also makes and sells cars in the USA, but is an "Intl equity". Both companies operate in the exact same place and make the exact same profits and sell the exact same stuff. Again, a theoretical example. The difference is that Toyota is based outside of the US, so the value of that equity will vary in the short term compared to Ford, but in the long term, they should be around the same. The advantage of splitting your portfolio in this example 50/50 Ford/Toyota, is that over the long term, your expected total return is the exact same. Let's call it 10%. By adding Toyota to the portfolio, it is likely that the gain/loss (unrealized) in the short term throughout the many years will swing back and forth...
you earn the same total return over a long period of time, but with lower volatility (our proxy for portfolio risk).
Again, in order to conclude that you are better off owning the Intl equity (Toyota) in addition to US equity (Ford), you have to shift your perspective from "maximum return" to "highest risk adjusted return". So, if someone offers you a portfolio with the same long term return, but with lower volatility, a rational investor should choose the mixed portfolio.
Hope that helps.