I'm sure they're attacks and attractive are AP the previous attached but that doesn't mean their AP is equal or greater than. Especially when you look at Kid's earning statement.
Last chapter, Kid talked about how water droplets can carve through stone with enough time.
That scene was explaining to us how the 2 Yonkos will be defeated.
Kid is telling it doesn't matter how powerful an opponent is or how much they seem to be invincible if you continue to attack and fight them then over time they will become worn out and defeated.
Their defeat won't come from a single character or two but from everyone who has faced them because it would have contributed to the Yonkos defeat. A water drop on a stone is insignificant but alot water droplets over time can carve out a stones.