Taylor Larimore thinks so. If you don’t know Taylor, he is a long-time Boglehead (i.e., a disciple of John “Jack” Bogle - the founder of the Vanguard Group). Taylor’s three fund choices:
a total market US stock index fund;
a total market stock International index fund; and
a total market US bond index fund.
That’s it. Pretty simple and the costs for such index funds are very low - a key determinant in improving an investor’s performance. Investing can be made simple!