I think you're taking quite an extreme interpretation of Graham's/Buffet's thoughts on index investing. It's a given that, with index investing, your returns will match the market. Index investing isn't aimed at getting higher returns. Rather, Graham actually spends more time discussing and differentiating between different classes of investors.

For the "enterprising investor", s/he can afford to spend more time to find undervalued stocks and possibly outperform the market. For the "passive investor", to paraphrase Graham, it is good enough to simply invest in a representative set of securities, such as an index.

In fact, if I remember my Intelligent Investor correctly, there are various passages where Graham actually admits to the EMH being somewhat inevitable. Note that there are different variants/degrees of the EMH, and Graham probably subscribes to the weak or semi-strong versions.

Nonetheless, the point is that a belief in the EMH is not mutually exclusive with value investing. It depends a little on the extent to which you believe the market is efficient, and a lot on how much work you're willing to put into it.