Isn't arbitrage slightly underrated by EMH?

I like your question. I trade in the financial markets and it would appear under the strong version of the EMH arbitrage isn't possible. However, I don't believe economists look to EMH as a perfect model but merely an approximation. Much like the rational expectations hypothesis only partially explains the slope of the yield curve; one needs to factor in risk premium to derive the complete explanation. Similarly EMH partially explains the price action we observe in markets. Arbitrage ists in the efficiency of markets by facilitating the flow of capital into its most resourceful uses.