You are confusing guessing with concluding. You can make certain conclusions with the facts you have now, and this is exactly what i did.
Ok then, reiterate for me. What exactly is your conclusion and how did you arrive at it based upon facts available at the present?
I can understand that Pokemon that are dependent on weather for success will suffer. Venusaur would obviously fall if Drought were banned, for example, since it depends on Chlorophyll to fulfill its given purpose. Gastrodon might also lose viability with Drizzle banned due to its niche of taking Hydro Pumps/Surfs and Thunders in Rain being eliminated. Not all Pokemon that can abuse weather are like that, though. For example, Jolteon literally just loses a reliable Thunder (I'd look up just how often Thunder is used on Jolteon, but the moveset stats appear to be down). It still has Thunderbolt, Volt Switch, excellent speed, Baton Pass, etc. Ferrothorn only loses its ability to somewhat help its Fire weakness, while meanwhile it still has Spikes, Stealth Rock, great typing, excellent bulk, etc. These Pokemon are not utterly dependent on weather, they just enjoy it.
The point is how many Pokemon can POTENTIALLY lose their viability on a Drizzle-less metagame
There is one other quirk with these arguments in that you have an inherent advantage since Drizzle is currently unbanned and we can see its effects. What I'm saying is that you can see which Pokemon are common in the Drizzle metagame and therefore you can make an educated (albeit unverifiable) guess as to which ones might be hurt by Drizzle's ban. However, we have no such observation as to which Pokemon might be more viable if Drizzle were banned, and so that's anyone's guess. While we could form a decent hypothesis as to which Pokemon would lose viability if Rain were banned, the number of Pokemon that would gain viability could be anywhere from a couple to many.
Many Pokemon can also potentially gain viability in a Drizzle-less metagame, but how are we to know just how many?
Whether or not the negatives outweight the positives or vice-verse is a discussion that could take ages, but the point is that it's not worth going for such a drastic change for something that can simply be solved with a single SIMPLE ban and its outcome can't really be predicted, as a Drizzle-less metagame has both positives and negatives compared to a Drizzle meta, unlike the metagame created after Aldaron's proposal, where we knew that there were practically no negatives after the combo ban was implemented.
And I would be inclined to agree with you if, say, Keldeo were the first Rain abuser being tested right now. The concern, however, is that we have made several notable bans at least in part because of Drizzle, and people are wondering if Drizzle wasn't the problem to begin with.
By banning the broken abusers you remove three OU viable Pokemon from the metagame. By making the combo ban you keep the OU viable Pokemon to be used outside of Drizzle and you still keep Drizzle in the meta, so you practically solve the situation with zero negatives.
As UltiMario pointed out, it's unclear as to how many Swift Swimmers would have actually been broken, but let's go with your number, three. If it were just the three, then we could have just banned those and let other Pokemon like Poliwrath, Gorebyss, Seismitoed, etc. have plenty of OU viability due to their niche with Swift Swim. However, by banning Drizzle + Swift Swim, what good did we actually do the metagame? People were concerned about losing manual Rain Dance teams with Swift Swim users, but how often do you actually see those now that all is said and done? How common are those Pokemon that we kept unbanned? Kingdra does enjoy noticeable usage, but that's about it. The Pokemon that we "saved" didn't actually have much of an impact on OU at all after the ban.
If it was just a small handful of broken Pokemon, would it not have been better to just ban those and leave the many other abusers with their niche rather than ban the combo and weaken all Swift Swim users with only one receiving even decent OU usage after the ban? In other words...
And banning 3 Pokemon to keep 12 and more Pokemon viable in the meta seems as the right decision to me.
...does it really?
Finally, you can't come to the conclusion that Drizzle was the breaking point of the Pokemon that were nerfed due to Aldaron's ban simply because both Drizzle and Swift Swim took equally big roles in making those Pokemon broken.
They did, but you cannot ignore that the bans of Drizzle + Swift Swim, Manaphy, Tornadus-T, and arguably Pokemon like Thundurus (Thunder) and Genesect (Thunder, lessened Fire weakness) had one factor in common: Drizzle. Regardless of what other factors might have made an impact, that was a common link between them. The concern is that all of these bans have been missing the main target, which is Drizzle itself (although Genesect and possibly Thundurus might have been banned regardless).
