Wanted to address this point as I think its pretty misleading to suggest that HP Fire Cresselia is running it exclusively for Durant, as HP Fire Cresselia (I believe it was OO on its analysis) also gives it a way to dent Doublade and Escavalier (I honestly think Escavalier is the culprit here, but I can't be sure as I'm not the user of that team).
Next, as stated by many people, Durant doesn't actually get that many chances to set up, given its status as a glass cannon, which, at least imo is why the Choice Scarf set is better, but that also has major flaws (the fact that none of its moves have over 80% accuracy is a turn off, at least Scarf Moltres has Flamethrower to fall back on, I pretty much only end up using U-turn and Flamethrower when using Scarf tres), such as being easier to wall due to Choice lock and also its STABs aren't nearly as spammable as Fire or Flying type moves.
As I've already stated (and pretty much everyone barring two people in this thread have agreed) Durant should definitely move up, but not to S rank. This comparison to Moltres is getting pretty dumb tbh, just because both Pokemon hit hard doesn't mean they are even remotely similar, thats like comparing Alomomola to Cresselia because they both have good defenses. First off, Life Orb Moltres hits slightly harder than Life Orb Durant with their STAB moves, Durant is really let down by the fact that its STAB moves only have 80 Base Power, so its X-Scissor, even with the 1.5 boost from Hustle, is hitting as hard as a Hustle-less Megahorn off of a base 109 Attack (the difference in Power between Moltres and Durant is barely noticeable, but I more so wanted to demonstrate that move BP is as big of a factor as Hustle or a High Attack stat). Secondly, Moltres has much better defenses (and both have pretty neat defensive typing o.o), alongside
reliable recovery, which not only makes it much harder to wear Moltres down, but also allows Moltres to perform a more diverse set of rolls, one of its best sets is the underutilized Sub-Roost Toxic Moltres, which puts a lot of strain on defensive teams. Next, while Moltres and Durant have a similarly limited pool of counters, Moltres's counters are both easier to deal with and much less viable in the current meta game (with 2ish exceptions). Lanturn, Regirock, Slowking, and Cresselia are the best switch-ins in the tier to Moltres. Lanturn and Regirock are both pretty uncommon (not that they aren't good) and pretty easy to wear down given their lack of reliable recovery, and susceptibility to hazards (I realize this works both ways but I assume a Moltres team will be more committed to keeping hazards off the field). Cresselia and Slowking (more so Slowking) can be U-turned on into a Pursuit trapper which makes them much shakier checks to Moltres than you would like them to be. Durant's top counters are Alomomola (neither of the above problems), Emboar (Choice Scarf or Fat Pig), Quagsire, and Moltres (Sub Roost, Choice Scarf I guess watch out for Rock Slide though, but Rock Slide is p shitty on Durant imo). These Pokemon fit on every play-style from full-stall to offense (same can't be said for Moltres's counters, which are much easier to fit onto stall / balance than offense) and are harder to wear down than Moltres's counters barring Emboar (also none are Pursuit trappable).
I agree with
tehy that froggyboy was using the weakest definition of a check (and that some of the Pokemon he listed weren't necessarily even that) but most were still technically "checks". And some of the calcs you were using were pretty bad, for example offensive Mega Steelix does much better against Durant than the version you posted, and more defensive variants are likely to carry roar, so Durant won't be getting to +2.
To clarify for everyone, a check is a Pokemon that can switch into at least one move that a Pokemon has and kill it before it is killed in return (barring hax) while a counter is a Pokemon that can switch into any move a Pokemon has and kill it before it is killed in return.
Durant should move to A+, Moltres is a better, more meta game defining Pokemon than Durant and will probably be staying in S rank, as it deserves to be.
This.