> Every asset class you just mentioned is already included in OP's two funds

While that is true, the long term performance of US Total Stock Market and S&P 500 is virtually identical, with a difference in return of 0.01%. (Yes I know VTWAX is total-world, just using US for simplicity's sake). Point being, the small/mid/value for example, are not a large enough percentage of the portfolio to make a meaningful difference.

Having said that, OP is perfectly fine as-is and need not change anything. However, a 10% "tilt" to US Small Cap Value (for example) would have produced an additional $300,000 in returns over the period 1972-2022. Link