*double facepalm*
Sure one guy could earn more than another, it doesnt mean everyone can earn more than 100% of available block BTC, that is whats up for discussion here.
If your efficiency for p2pool displayed 200% efficiency then there must be another user with same hashrate getting 0% efficiency and mining into your wallet.
If everyone could easily get >100% efficiency as electricmucus suggested, where do you think that extra magical BTC comes from within p2pool network ? Surely not from space and time itself.