In old school baseball, I'd say so, but in today's game you don't need the leadoff batter to hit for average the way you used to. Obviously it helps, but there's seven guys in the lineup capable of going yard in any give at-bat. In todays home run era, so many different guys can generate their own offense that it doesn't matter as much if one guy's cold.
What's so impressive is that, even with the strong offense we have, is that Mookie really is the difference maker