[TheWorstPlayer]

Just because he only has neutral EV decisions against you doesn't mean that he can't make a mistake. The way in which he chooses between the neutral EV decisions with which he is presented can (and likely will) allow you to make a +EV decision which will again leave him with a neutral EV decision. Obviously this is easier to see from a limit perspective due to the limited strategy space. For example:

You have KK UTG and raise. He calls in the BB. Flop comes JT6r. He checks, you bet. Now ideally should be making this exact same sequence of moves on this type of board with enough hands such that your hand range here should be large enough that all three options (raise, call, fold) are neutral EV. This must be the case because if, for instance, folding were preferable, then you should start taking this line with more hands to exploit the fact that he is folding too much. Once you start adding more hands, he will have to start calling more since he will be ahead more often of your widened hand range.

So let's say that your hand range here is such, in fact, that he only is presented with three neutral EV options. However, let's say that every time he has better than top pair, he raises, every time he has top pair he calls, and every time he has worse than top pair he folds. So even though you perfectly balance your actions so that he can't make a +EV decision based on your hand range, his action gives away so much information about HIS hand range that your next action will be +EV for you since he is not properly balancing his strategy.

But again, your response to his action should be perfectly balanced so that again he has only neutral EV actions. Basically, every time he does something that gives you information which you then use to put yourself onto a +EV course. Your actions, however, are perfectly balanced so that HE gains no information from your actions and therefore cannot steer the hand into a +EV course for him. That is how you are playing perfectly against him and he is not playing perfectly against you.

Edit: It should be clear that you can't possibly provide someone with a -EV option without also giving them a +EV option. Therefore, perfect play must entail always providing only neutral EV options.