Rate limiting and bot blocking are two totally different things. Rate limiting only increases the cost of a bot attack. Either they need more IP's (which are dirt cheap in the black market) or they need more time--either way it is increased cost. But it won't stop a bot. Just slow it.
Banning IP's might have worked back in 2000, but these days it is useless. Bypassing an IP block is trivially easy for even a low-sophistication attacker.
