First, lets be very clear on this:
We created a Threats List, not a Counters list.
If Dusk wants to argue he submitted a stat spread with 131 SpA on the assumption it wouldn't trample over Landorus, Gliscor, and Duggy if they switched in during any weather condition other than Rain he can do so, but really: We're encouraging Mollux not to be used in Rain if we don't give it functionality in Rain.
Actually I know that's not the case and that it'd be fine since he submitted the spread under the assumption Drought would win, and it did not, so you'd have a bit of duality there you can play with. No such duality now exists, and I'll say it again its my fault for not requesting a Counters Discussion after Ability was selected anyway - not that I ever wanted it removed, but what's past is passed.
Mollux was built ostensibly as a Fire type that could mess with Rain by virtue of loling at Bulky Waters with Ice Beam and Toxic, while also keeping Ferrothorn and Scizor out with Fire STAB, even if weakened in Rain. That was the premise behind the typing. That is something it can accomplish, but then what? Then you have to use Poison STAB in Rain and you run into a very large wall of truly hard counters. Part of being OU is being able to perform in your niche, and the niche presented without Scald is fairly small. You end up with a Rain-loving Pokemon incapable of using Rain effectively, and the Burn chance of Scald is quite important, because Scald gives it a means of Burning foes without being forced out if the move doesn't burn, like Lava Plume would on anything that switches in during Rain.
This leads to an odd dynamic where you actually run things like Landorus/Gliscor/Duggy in Rain because you know Mollux is no threat since its only relevant offensive STAB gets halved in Rain. I don't think that's a healthy dynamic, and I think like the frets over Pyroak's walling capabilities, the frets over Scald are overblown. Ironically without Scald, are Threats are only true Counters in Rain, which is playing against their own style. Switching in Tyranitar actually *decreases* in value because in Sand, Mollux can obliterate most of those checks with Fire attacks.
Our check list (bar Tyranitar which hates Burn in all its forms) is already "smashed" circumstantially in Weather, with Sun allowing it to nuke Terrakion with Solarbeam (Solarbeam being balanced by being terrible everywhere else), and everything else getting exploded by a boosting Fire move. Heck, in the next phase if we allow Flame Charge for the Speed boost, the irony will be sweet. Let's be clear here, if we want to talk about our Threats List, every last one of them, Scald or no, is still a Check, with Tyranitar being the only Counter. All the other true Counters find themselves among the like of Latias, Latios, Hydreigon, Dragonite, and Gastrodon for which the only answer with our coverage options is Hidden Power. I'm comfortable with that, since bar Gastrodon every last one of them is faster and can do competent damage inside and outside of Rain.
An additional wrinkle is the role of Sun teams and Grass types. If you're running Water/Electric/Poison and forgo your Fire move because you assume Rain, you get boxed in by Grass/Poison types, especially Venusaur. Even Ninetales can give you trouble if your Electric move was Thunder, not Thunderbolt (same with Heatran, who lols as unSTAB Scald in Sun). Dry Skin's HP erosion along with boosted Fire in Sun is not pleasant. That's in general why I like Scald. I'm well aware it will be used, I just feel its effects are negligible considering the only thing it does is punish Mollux against Pokemon that would otherwise think twice about switching in during any weather other than the Rain teams we set it up to mess with. It can't control weather without using a move, so there's no sense in making it operate in Rain poorly against things it normally would be able to stave off.
I was a bit remiss with Final Gambit. It's pretty cool and definitely competitive with an HP Gaining ability and 95 HP.