As a note I'd just like to say how Durant can beat Quagsire with Band set, see:Durant A- to A: Agree
I feel like Durant didn't get too much attention this generation so far, being overshadowed by the UU mons dropping from Oras. Taking a look at the pokemon in the S to A ranks in the ranking, Durant beats the majority off them with it's stabs, Superpower and Crunch. While Durant has a good portion of counterplay in this meta, actually most of it's checks can be defeated with the right coverage moves and I think the metagame shifted in Durants favor lately. Let's take a look at Durants most common counters:
Fire Types: aren't as common or versatile like they've been in earlier stages of the metagame, Camerupt-M and Emboar dropped down in viability. The only Fire Types in S to A- rank are Moltres and Salazzle, and Moltres gets killed by a Rock Slide while Salazzle beats Durant for sure.
Doublade: Basically beats every Durant variant without Crunch, namely the Choice Scarf set. Life Orb Durant has a good chance to 2HKO Doublade, and Hone Claws Darkinium Z Durant beats Doublade anyways. While being forced to run Crunch isn't a great thing, losing at least one of X-Scissor, Rock Slide and Hone Claws depending on the set. But 2 of 3 common Durant sets can beat Doublade.
Bulky Water Types: Aren't as common anymore with Mantine leaving the tier a time ago. While Milotic can be beaten by using the uncommon Z-Thunder Fang Set or , Quagsire beats Durant all the time.
252 Atk Hustle Durant Gigavolt Havoc (120 BP) vs. 252 HP / 136 Def Milotic: 360-424 (91.3 - 107.6%) -- guaranteed OHKO after Stealth Rock
Gligar I feel is more problematic for Durant than Doublade, because none of it's common sets can beat Gligar, allowing it to setup Rocks or Defog, there's still an option to beat Gligar with Durant by using the Hone Claws Set with a Steelium Z or by going for the Darkinium Z Hone Claws and just using Iron Head. This might be a little over the top in a VR post, but assuming you go for Hone Claws while Gligar switches in or uses one of it's utility moves:
Darkinium: +2 252 Atk Hustle Durant Iron Head vs. 252 HP / 252+ Def Eviolite Gligar: 160-190 (47.9 - 56.8%) -- 90.6% chance to 2HKO
Steelium: +1 252 Atk Hustle Durant Corkscrew Crash (160 BP) vs. 252 HP / 252+ Def Eviolite Gligar: 241-285 (72.1 - 85.3%) -- guaranteed 2HKO
+1 252 Atk Hustle Durant Iron Head vs. 252 HP / 252+ Def Eviolite Gligar: 121-144 (36.2 - 43.1%) -- guaranteed 3HKO
Durant beats a lot of the bulky/defensive pokemon in the tier, Registeel, Snorlax, Doublade if running Life Orb or Z-Crystal with Crunch, Cresselia, Umbreon, Gigalith and Milotic if running Z-Thunder Fang.
252 Atk Choice Band Hustle Durant Superpower vs. 252 HP / 252+ Def Unaware Quagsire: 208-245 (52.7 - 62.1%) -- 99.6% chance to 2HKO after Leftovers recovery
Fightinium Z also has a shot after some damage (as well as Darkinium after more damage)
252 Atk Hustle Durant Superpower vs. 252 HP / 252+ Def Unaware Quagsire: 139-164 (35.2 - 41.6%) -- 81.4% chance to 3HKO after Leftovers recovery
252 Atk Hustle Durant All-Out Pummeling (190 BP) vs. 252 HP / 252+ Def Unaware Quagsire: 219-258 (55.5 - 65.4%) -- guaranteed 2HKO after Leftovers recovery
Unaware ignoring Attack debuff is annoying, Gligar is also very shaky cuz its not going enough damage to beat Hone Claws sets and Fightinium Z also KOes Milotic after Rocks (~94%), defensive counterplay to Durant is barely a thing, with Spikes Quag might just lose, Ampharos-M dies to +1 Dark/Fight Z, a healthy Durant can setup once or twice on Gligar cuz with luck the bat is only 3HKOing, revenge kill Durant is the way to go, for teams without Salazzle your options are Scarf Moltres, Specs/HP Fire Espeon (Specs needs Rocks to KO 100% of the time), Swellow, Scarf Moltres, Shay and some other Scarfers, I wouldn't even disagree with Durant to A+, tihs thing has very limited counterplay and can usually bypass even its best checks (see Quag) after some prior damage, and btw with right prediction Band 2HKOes everything in the meta which is why I agree with it rising.
Now about Tsareena, I tried to find a niche for it, it fails to beat Feraligatr, Bruxish, and any Offensive Water-type, Defensive sets loses hard to Regi, Zong and Queen while Offensive ones must HJK Regi in the right turn and are still beaten by Zong and Queen. Its weak and can't beat Doublade or Decidueye, they can not only spinblock on it but use it as a fodder, even without Ghosts on the field its not a good mon to Spin, the only decent niche I ever found is that Tsareena can counter SD Aboma and I don't see how this is enough to keep it ranked, agree with it unranked.
And I'll just give my opinion in some noms:
Feraligatr to S overrates the aligator, its a great mon but it will have a hard time breaking Milotic and Chesnaught, most Scarfers can beat it, should keep A+ because its really good but not meta defining imo.
Also imo its funny try to put a mon into S and its best answer into A-, well...Milotic will struggle with Grass-types which is annoying but its still very bulky, a great Gatr and Doublade check, can beat a Flygon that already spent its Z, can prevent Lax from sweeping with Curse, taking Toxic is annoying but it will also boost Milotic's already nice Defense. The point that it struggles against some threats is like Regi struggling with Salazzle, Queen, losing to SD Zoroark, never touching Doublade at all (all A+/S mons) and its still A+, imo keep Milotic where it's at rn cuz I've been using it so much lately and its still working very well.
Oh and btw I agree with Roserade to A+, this mon is so nice and annoying to play against rn, Spikes are broken its STABs are very powerful and Technician HP is so great giving you a "Flamethrower" or an "Ice Beam", Scarf sets are also very nice since its really strong and can revenge kill threats such as Salazzle and Swellow.