Alright, since I'm in the mood atm I guess I'll reply to this list of proposals.
I think Skuntank should go up, C+ is pretty insulting for its capabilities. It's a cool Defogger that provides decent defensive synergy and packs a decent punch too. It checks quite a few threats such as Reuniclus (!!), Meloetta, etc. and can use Defog reliably. It also has extra nifty utility with Sucker Punch and Pursuit which allow it to get in some mindgames with some Pokemon and can revenge kill or trap: it's sort of weak, but it hits hard enough for what it does. I know Drapion has the same typing, but it doesn't have Defog or Sucker Punch like Skunk and actually plays somewhat differently from it. It's a pretty good Defogger and should be at least B- imo.
Not commenting on Granbull, but B- wouldn't be a bad idea at all given it's one of the most reliable Hitmonlee answers in the tier and is more bulky than the other Fairies in RU with Intimidate factored in and it's also one of the few physical Fairies other than Slurpuff who plays differently: it has a nice movepool to use on both worlds too.
No comment on Seismitoad
Sceptile...ah the poor thing I haven't really used much since like the beginning of the generation. It kinda faces really stiff competition from Virizion these days, and it's rather easy to deal with by using stuff like Escavalier, Druddigon, etc. It's kind of weak and it's not really as impressive as Virizion. I guess C+ would be okay since it's not really bad but Virizion gives it pretty stiff competition.
Not commenting on Audino or Gastrodon because I don't have much experience with them, Gastro is a pretty good Doublade answer though and it also takes on HP Water variants of Jolteon quite well unlike Rhyperior or Slowking so that's a pretty strong niche for it.
Tyrantrum...I dunno man...I kinda like it. It's a decent physical sweeper that hits hard at +1 and has an okay Speed to sweep with Dragon Dance. It has nice coverage too in EdgeQuake as well as Ice Fang, so it's one of those physical attackers that has a fighting chance against Gligar. Only problem is that it kinda has trouble setting up and depending on its nature it kinda is either a bit slow or a bit weak (I prefer Jolly though). It also checks Moltres and Fletchinder which is totally awesome, and it's a fine sweeper. I want it to stay in C+ tbh. It shouldn't be in the same rank as Barbaracle, Tyrantrum is honestly quite a bit better than Barbaracle at sweeping and it checks bird.
Gallade is kinda okayish, it's pretty decent but just kind of outclassed. It's pretty good at what it does tbh and SD and other sets are kind of cool. I'm not really a huge fan of dropping it since I feel like the B Ranks suit it pretty well.
I'm really not a huge fan of dropping Cinccino down. Cinccino is honestly actually a pretty decent Pokemon and is not really a C+ Pokemon in my eyes. It's very fast, and has three high BP moves that are multi-hit, so it hits pretty hard and bypasses Substitutes and Focus Sashes. It circumvents Rhyperior, Moltres, Fletchinder, and a myriad of other Pokemon thanks to its decent coverage and power. It's quite tricky to handle for all of offense, balance, and bulky offense. For that last moveslot, Cinccino can always run something to be all the more tricky. It can run U-turn to nab momentum, Knock Off to cripple Doublade, and let's not forget the mighty Sing which cripples Doublade and renders it useless (it will always hit thanks to No Guard!!), and from there Cinccino can proceed to pester the opposing team. It's hardly a bad Pokemon and shouldn't drop imo, when played correctly it is quite tricky. Did I not mention this thing is the cutest thing ever!!!
Tangrowth I have no opinion about but it's a bulky thing and even though it doesn't have that many resists, it tanks nicely by sheer bulk alone, it has Regen and solid offensive presence too so that's a bonus.
Regirock and ROCK WITH EYES can move up, the former is a nice Moltres answer and also beats a few other Pokemon like Cinccino, DRUDDIGON, etc by its resists as well as its sheer bulk. Carbink I'm not completely solid about but it's nice for stall and handles a horde of common Pokemon that otherwise pester stall.
Golbat can be B+, since it's a pretty good Defogger that has very nice bulk and it takes on Hitmonlee and Aromatisse quite nicely. It's vulnerable to Knock Off but its typing, Defog, bulk, and okay offensive presence make it quite solid.
Hitmontop I have no opinion on, though it can be B-. Intimidate is a really cool ability and allows Hitmontop to check and lessen the threat level of many physical attackers in the tier, and with Foresight it can both get a spin on Doublade and stand a fighting chance against the two swords by hitting with Close Combat. It has fine bulk to spin with and Foresight is nice for something with its bulk, it's a more bulky spinner compared to Hitmonlee and Kabutops so if you need a more defensive spinner Hitmontop is definitely up there.
I definitely think Clawitzer should move up. I've used it since the beginning of XY RU, and it's really awesome. It packs a real punch with 120 Special Attack and Mega Launcher, plus awesome coverage in Scald, Aura Sphere, Dark Pulse, and Ice Beam. It packs a lot of power with these three moves, and is very hard to switch into. This makes Clawitzer a really good breaker that can also provide incredible offensive pressure to the opponent's team, and it has okay bulk to use as well. Every slower mon is basically going to have trouble facing Clawitzer and this thing hits hard. Even though it's rather easy to wear down and revenge kill, Clawitzer is really good at wallbreaking and applying offensive pressure so it should be A- imo.
Idk about Registeel, it's kinda not as good without Yanmega but it's still a great wall, and Emboar is still a decent breaker so I don't really know what to say.
I said this before but Bronzong should move up. B- is less than it really deserves. It's a very good bulky Steel-type that makes for a reliable SR setter, and packs a decent offensive presence with Gyro Ball and Earthquake. It's a great Abomasnow answer and it takes on Rhyperior decently and in general has a horde of resistances to switch into quite a few things. It should definitely be B Rank if not up there in B+, very undervalued Pokemon.
Won't comment on the others though I'm really not a big fan of dropping Durant, it doesn't require much support to function and it's really freaking scary, if you let it set up once (which isn't that hard), it will basically destroy you.
Just some thoughts.