The Pans and the Lord of the Wild pretender have the same turmoil summon effect. It doesn't have a power attributed to it, just says what kind of unit it summons. The only way to increase the output of the turmoil summoning is to let a unit have the effect twice or more times, and indeed the Lord of the Wild has that ability listed twice. So he's twice as effective as a Pan to draw Maenads, or rather as effective as two Pans.
I didn't mean you get stronger maenads (even tough I now can see it could be read that way, can't edit that anymore sadly), I meant it is better for the number of maenads the stronger the Turmoil is in the province