Let's say Sanji didn't use sneak attack. Sanji kicked Page One, Page One groaned in pain. Page One attacked Sanji, Sanji felt little pain. Again Sanji kicked Page One again Page One groaned in pain and took more damage. Page One sent Sanji flying again Sanji only felt little pain and it is clear who takes more damage, Page One even if Sanji didn't sneak attack lol.
Not equal when Page One took more damage lol and already explained above.
It matters if the enemy felt more damage than the attacker. Page One in this case is the enemy and he took more damage than Sanji lol. Apoo is just a bad match up for Luffy and co.