While I get what you're saying, I don't think that we should default to banning the weather abilities. I find that only one sand Pokémon finds it sufficient to have support from a sand team, namely Landorus, as opposed to Excadrill/Doryuuzu, who I find basically needs sand to be up to function. On the other hand, by banning Sand Stream, we ban Tyranitar and Hippowdon by technicality. So I see banning the Pokémon as the simpler solution, even if Excadrill/Doryuuzu were banned as well.
Rain is kind of a different beast, though. Kingdra is bulkier than Excadrill/Doryuuzu, enough to be pretty significant, and has pretty beastly defensive typing and STAB coverage, while Ludicolo also has beastly defensive typing and STAB coverage, both in contrast to Excadrill/Doryuuzu's primarily offensive stat/typing structure. I'd argue that they don't require rain up to function as much as Excadrill/Doryuuzu does. (This is different from support from a rain team; I'd happily agree that Ludicolo sucks outside of a rain TEAM, but if push comes to shove it's not dead weight if rain happens to be down for a while.) Versatility on both of their parts helps a lot. We could ban them both and possibly even Kabutops, but banning Drizzle is actually the simpler route in this case because Politoed isn't banned by technicality. And this is why I am personally inclined to treat sand and rain differently.
On top of this, we're "pretty sure" that the loss of Landorus and possibly Excadrill/Doryuuzu would be enough of a hit to sand to prevent it from being broken. We don't have the same assurance for rain, and while it can't be made for certain that it *would* still be broken, this uncertainty in comparison to sand is enough to sway people toward treating the two weathers differently. As far as argument goes, last is least here, but I think that it needs to be said.