Pike will/can still bite through the lighter weights of
fluorocarbon leader.
If they didnt, I would use 20 - 30 lb for pike rigs. I dont use less than 40 for pike.
But it will help at any weight(its much better than mono of same weight).
The higher the weight you go in fluoro leader the better it is at being bite proof.
Titanium and steel leaders are bite proof.