Okay, I'll address why a majority of the council currently thinks Cherubi is the mon to ban.
Firstly, I don't think any solutions outside of banning Cherubi or Vulpix should even be considered. To clarify, Chlorophyll was brought up in the council chat in the context of a later metagame that potentially has Bulbasaur, not what we plan to do about the current metagame. I don't think Chlorophyll was actually the first choice to ban for anyone (please correct me if I'm wrong); myself/tazz/star/coco/ninja lean toward a Cherubi ban, fatty/kingler lean toward a Vulpix ban, and quote/shrug are undecided.
Tiering with Bulbasaur in mind doesn't make sense when it's not even released. We have no idea when it'll be released, nor the circumstances surrounding its release; for all we know, it might be released in a radically different home meta, or it might even be an unbreedable level 10 event Pokemon that isn't available in LC. There really isn't a point in trying to tier with a mon that doesn't exist in current LC and may continue to be absent in the foreseeable future.
And if Bulbasaur does get freed with its full movepool in a relatively short timeframe, into a metagame where Drought Vulpix is legal (and Cherubi isn't), then we will know beyond a
reasonable doubt that Bulbasaur is broken, because Cherubi is broken and Bulbasaur is better than Cherubi in every way that matters. This means that we can alter the banlist as we see fit with the full understanding that Chlorophyll Bulbasaur + Drought Vulpix must be disallowed in some form. There is no benefit whatsoever in trying to tier for a Bulbasaur metagame in advance instead of waiting for its actual release.
With that in mind, banning a non-Pokemon trait becomes much less worth considering. I realize that a Drought ban was mainly only brought up in response to Chlorophyll being on the table, but I'll briefly address it anyways. A Drought ban is less ideal than a Vulpix ban by our current tiering policy because in most cases, we try to tier Pokemon. It helps here that banning Vulpix and banning Drought are almost completely equivalent - Vulpix has no viability without Drought, so we gain nothing from trying to preserve Droughtless Vulpix. In either case, we're removing Vulpix from the equation entirely (but banning Vulpix is preferable policy-wise).
A Chlorophyll ban is even less of an option in a Bulbasaur-less metagame. Not only is it worse policy-wise - we'd be banning the ability instead of the mon - but it'd literally just be banning Cherubi with more collateral by eliminating manual sun, because Chlorophyll is Cherubi's only legal ability.
Heat Rock is not being seriously considered for a ban because it's unlikely that it would solve the issue at all; Vulpix would still be nearly as capable at maintaining Sun throughout the game when wielding a defensive item like Berry Juice or Heavy-Duty Boots.
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I do not believe that a Vulpix-Oddish core would be broken, and I don't think Oddish and Cherubi are even comparable in terms of threat level.
Oddish and Cherubi flat out do not share a majority of their checks. This isn't like last gen, where every Chlorophyll sweeper had almost the exact same checks; Bellsprout was just slightly better at dealing with them because Weather Ball was stronger than Hidden Power. Oddish's STAB options consist of Grass and Poison. This leaves it walled by most Poison- and Steel-types + Drifloon, which is a reasonably large group of Pokemon that includes its fair share of defensively valuable mons or generally viable mons. Grass/Poison is honestly kind of pitiful as coverage for an offensive mon, and as a result, Oddish is fairly straight-forward to accommodate defensively. Its main advantage is Sleep Powder, which is both unreliable and burns the valuable Sun turns that Oddish needs to sweep.
On the other hand, Cherubi has Grass and Fire pseudo-STABs, and Fire is among the best offensive typings in LC. The defensive checks of Cherubi are limited to bulky Fire- and Dragon-types. There are no Dragon-types worth serious consideration (or aren't total liabilities outside of resisting Cherubi). Fire-types are weak to Stealth Rock, and most have low defensive stats + no recovery; the sole exception to the latter is Growlithe. The list of defensive answers to Oddish and to Cherubi aren't even remotely close in scale or quality.
Vulpix as a standalone threat is almost surely not broken. Non-scarf Vulpix's speed tier isn't terrible, but it's too low for it to be classified as a serious sweeper; as a wall-breaker, it carries substantial defensive answers in Mareanie and Munchlax, both of which would likely be among the best defensive mons in the game regardless of Vulpix's presence. Choice Scarf Vulpix isn't unstoppably powerful - its Timid Fire Blast is roughly as powerful as Jolly Farfetch'd's Close Combat, for reference - and on top of still being walled by key defensive mons, it suffers from being vulnerable to every entry hazard.
So the issue isn't Vulpix as a standalone mon, or Cherubi as a standalone mon, or the Vulpix + Oddish core, or even Vulpix + dual Chlorophyll. The issue lies strictly in the Vulpix + Cherubi core, which allows Cherubi to gain doubled speed AND a Fire-type pseudo-STAB without the defensive drawbacks of carrying a Fire typing, immediately upon switching in without the need for a manual setter. Cherubi would not be broken without Vulpix's support; equivalently, Vulpix, Oddish, and the Sun archetype as a whole would not be broken without Cherubi.
Only with the understanding that banning Vulpix and banning Cherubi are equal in terms of tiering policy, and that both solve the issue at hand of Vulpix + Cherubi, can we start considering other factors. I'm sure we can all agree that the result of a Vulpix ban, which is a spin-less Gossifleur in Cherubi, is not going to be very helpful to diversity; compare this to the result of a Cherubi ban, which is a decent (but not broken) wallbreaker in Vulpix, as well as a neat (but not overbearing) archetype in Sun.
However, this is all assuming that Vulpix + Oddish is indeed not broken, since then we would want to keep them to encourage diversity. If Vulpix + Oddish is a problem (as fatty and kingler believe), then of course Vulpix would be the mon to ban to actually solve the issue (which would be Vulpix + Chlorophyll, not Vulpix + Cherubi). And if that is the case, then I'm ultimately okay with taking the chance and admitting that we wasted a few extra weeks to discover that we'd initially misread the problem.
That's possible but I believe at some point in the Discord Quote said the council unanimously agrees something needs to be done about sun, so arguing for/against this isn't gonna do anything anymore.
It's true that all of us currently believe that Sun needs to be dealt with, but it definitely wasn't meant to be construed as a reason to ignore that aspect of the discussion. Please don't be afraid to try and argue against Sun's brokenness if you think it's fine.
We're discussing Drifloon as well, but it hasn't seen as much discussion just because Drifloon took longer to come online as a potentially suspect-worthy threat (whereas Star's team already used sun like twice during week 1 of ekans). Feel free to give your input on that as well!