Actully, politoed can do more than just bring rain. It's specs set can be devastating with hydro pump. Ninetales kinda fails to do this, however. Unlike poli, ttar and hippo, it's not gonna win the weather war on its own, it needs support. (In this case, weather trapper tran.)
Specs Politoed isn't really a threat most of the time, it's drizzzle itself, I actually switch sdef tales INTO hydro pumps, because unlike keld, it's not that strong after being neutered by sun:
252+ SpA Choice Specs Politoed Hydro Pump vs. 252 HP / 232+ SpD Ninetales in sun: 182-216 (52 - 61.71%) -- 95.31% chance to 2HKO
252+ SpA Choice Specs Politoed Hydro Pump vs. 4 HP / 0 SpD Sawsbuck in sun: 84-99 (27.81 - 32.78%) -- guaranteed 4HKO
252+ SpA Choice Specs Politoed Hydro Pump vs. 72 HP / 0 SpD Venusaur in sun: 63-74 (19.74 - 23.19%) -- possible 5HKO
you get the point by now
Politoed's only viable because of drizzle, face it, you can argue all you want but we know why that thing jumped from DPPt NU to BW OU: Drizzle.
Taking anything else into consideration other than it's support for the rest of it's team defeats the point of it being up there, Toed is S because it brings the most mindless "powerful" weather (imo sun is better but these are the ramblings of a mad man) into play, not because of it's specs set, heck defensive toed contributes more because it simply doesn't overlap with things like keldeo and can actually support the team by toxicing and scald burning possibly dangerous foes to the team.
Ninetales has 2 very important things that it brings that it contributes to drought teams: checking volcarona (sdef set) and *fast* WoW (fast support set or sdef set)
Ninetales's Special Defensive set or even it's defensive set from it's analysis (sdef tales isn't on the analysis page qq ;-;) can combat volcarona, probably one of the biggest threats for sun, why? because if sun doesn't get up SR, then +2 volc basically is a win for the foe. Ninetales, Heatran and even Arcanine all check volcarona, making htem all valuable assets, but why waste a another slot on checking volc when you have something that's your weather starter that can check it, this means not only does ninetales support a team with drought, but it also can support it's sun teams with checking volcarona and other threats.
All in all, Ninetales bringing the best and most powerful weather in OU should be enough for it to be S, people just like to whine about how SR weakness is the apocalypse honestly(no offense). Sawsbuck, Venusaur, Lilligant and more actually have a purpose in OU due to this thing, and hell are they amazing. Sawsbuck and Venusaur would be A and S respectively if ninetales was S, because lets admit it, when have you not been threatened by those two when a competent player is using them? Seriously, sawsbuck can actually run excadrill's old spread from back when it was OU and make scarfs irrelevant from your opposition, +2 buck HURTS, seriously, (jump kick is what I recommend because baloontran and ferrothorn are bitches :[) even unboosted LO sawsbuck hurts offense pretty hard, OHKOing DD dnite after SR and offensive QD volcarona regularly:
252+ Atk Life Orb Sawsbuck Double-Edge vs. 4 HP / 0 Def Dragonite: 243-289 (75 - 89.19%) -- guaranteed OHKO after Stealth Rock
252+ Atk Life Orb Sawsbuck Double-Edge vs. 4 HP / 0 Def Volcarona: 331-391 (106.08 - 125.32%) -- guaranteed OHKO
Overall, sun is possibly the BEST current weather in OU due to how much different chloromons and fire mons you can abuse while still remaining viable, Sawsbuck and Venusaur absolutely demolish teams, victini and darmanitan break insane amount of walls, volcarona makes OU tremble in the proper conditions, etc.
BUt as long as people like to say "SRSRSRSRSRSR", we will never have S rank ninetales, but hey, I sure as hell will NOT let it drop to A rank