There is a good reason why Swift Swim + Drizzle got banned but both Chlorophyll + Drought and Sand Rush + Sandstream are still allowed.
To make it short, most Pokemon that have access to Swift Swim are Water-types, mean they not just double their speed but also gain double STAB boosts (by typing and Rain boost). In contrast to this, there's no Pokemon that has Chlorophyll while being a Fire-type, so no double speed along with double STAB boost. Sand Rush users don't even receive any power boost by Sand (however there's an ability called Sand Force to increase Power but keeps the speed stat where it is).
Long story short: There's a good reason why Swift Swim isn't allowed along with Drizzle and why it should stay banned from OU and obviously lower tiers.
i got a question, why is shift swim with drizzle ban from ou? i don't see the point if chlorophyll is not ban with drought then why is drizzle with shift swim i propose a petition if the rules were that we can have drizzle with one shift swimer per team allowed, i think that is fair,think about it the BW2 metagame needs to have more interesting factors like using the shift swimmers like kabutops or ludicolo, i think it would be more fun to use some of the forgotten pokemon that have potental to sweep and to make the pokemon community fun again to create more strategies