all of those are definitely not deserving of higher than B+
Mamoswine and Salamence both live in the shadow of Landorus-T, and are therefore unimpressive; Salamence is definitely the better one of these two, since it usually runs a special attacking set, which sets Tailwind very reliably. I'd probably go with mence in B+ and mamoswine just to stay in B. Also to add to the Mamo hate, base 80 Speed is a super awkward position for a Pokemon that essentially needs to run Life Orb (can't run Sash efficiently like Loom the Spore spammer).
Thundurus-T is another Pokemon that is very much beneath one of the stars in Doubles, which is Thundurus-I. Thundurus-T's bulk is near unusable, it's as simple as that, but Thundurus is generally seen as better since it can attack viably whilst also supporting with Prankster Thunder Wave / Taunt. While Thundurus-T does hit notably harder, it doesn't even come close to the versatility that Thundurus can pack (Thundurus-I can run both offensive and bulky, and both of the sets can support the team whilst dealing damage).
Also for perspective: Sylveon, Ferrothorn, and Rotom-H are all notably more viable than pretty much all three of those Pokemon (mence comes close though)
With that I would like to nominate Hitmontop for B, and if possible, I'd like to nominate Scrafty for B again, since a lot of the reason people disagreed last time, was that they thought it was a slightly better Hitmontop. Will-o-Wisp is flipping everywhere right now, and these two Pokemon are straight up turned into free turns once burned. Aside from still being able to Intimidate + Fake Out, that combination of ability + move is ridiculously easy to just switch out from properly and you can then completely shift the momentum in your favour.
Seriously, these Pokemon are pathetic when burned
136+ Atk burned Hitmontop Close Combat vs. 252 HP / 44 Def Rotom-W: 71-84 (23.3 - 27.6%)
136+ Atk burned Hitmontop Close Combat vs. 4 HP / 0 Def Terrakion: 171-202 (52.7 - 62.3%)
-1 224 Atk burned Scrafty Ice Punch vs. 4 HP / 0 Def Landorus-T: 90-108 (28.1 - 33.7%) - this is fucking ridiculous
224 Atk burned Scrafty Stone Edge vs. 0 HP / 4 Def Talonflame: 218-258 (73.4 - 86.8%)
224 Atk burned Scrafty Knock Off (97.5 BP) vs. 4 HP / 0 Def Latios: 145-172 (48 - 56.9%) - this is STAB SE, and doesn't even 2HKO
Basically both of them are weak as shit, Scrafty doesn't even Wide Guard, so it's COMPLETELY useless when burned, and when burned, they generally fail to do what wins battles aka deal damage.
tl;dr, these mons are not A rank material in a metagame where even Talonflame runs Will-o-Wisp. Also Knock Off Scrafty is overrated, that move succeeds best of anything at Stallbreaking, which is irrelevant in Doubles.
edit: I also have a large announcement to make
EVERYONE FROM PS STOP USING SCALD KELDEO, IT'S SO TERRIBLE
and I didn't even get burned by it yet