Against most physical both don't do well. While most of the matchups were true, they are not alone enough. Glowking has the ability to fish for poison and has pretty neutral if not good matchup against many threats rn. Slowking vs tran is p difficult as even if you have eq, you have the potential toxic from tran which ruins the mon. And slowking was only used to come in eat, fs and tp. Meanwhile, glowking can flaunt its movepool while having the bulk to shrug hits with ease. Slowking does not "beat" the mons which it actually it switches in to. Lele does not care about scalds, you cant touch volcanion, bulky volc can eats scalds,(idk why you are using tail but it could possibly beat volc which is not maxhp max def). But even then lele has a minute chance to beat you with psyshock assuming timid, If its modest psyshock, glowking at least prevents a free switchin but slowking walls it fs but does not prevent most mons coming in for free because it soo passive. I would not go as far to b-. But b+ would be fine imoThe Slowking hate is way too overblown. I am mostly going to do a direct comparison with galar king since that seems to be the direct competitor for it in everyone's minds.
The first thing I want to mention is that slowking can run an assault vest set. I'm not saying it is the best sking set but let's see how different it is from the normal av galar king set.
Slowking @ Assault Vest
EVs: 252 HP / 32 Def / 224 SpD (Evs can be optimized)
- Aqua Tail / Scald / Razor Shell
- Future Sight
- Flamethrower / Other Coverage
Like galar king, slowking can pivot with av, run future sight for team support, scald for annoyance purposes and even stuff like d tail since it isn't as easily walled by steels so the only thing that actually matter will be the match ups. Thus, to be inferior to av gking, the thing that will mostly matter will be the matchups. Let's look at it's performance against the entire tier.
Ordering the matchups by viability
VS: AV EQ king is the best heatran counter in the tier. It has the longevity to sponge off hits infinitely, can 2 shot it with eq regardless of the set and can even heal off chip from magma+tox without caring about taunt due to regen andthe attacks dealing like 10% damage. You can even take a knock off from pex or ditch eq for other moves and still be fine to an extent! It is that bulky.
252 SpA Heatran Magma Storm vs. 252 HP / 224+ SpD Assault Vest Slowking: 38-45 (9.6 - 11.4%) -- guaranteed 4HKO after Stealth Rock, 1 layer of Spikes, and trapping damage
On the other hand, galar king needs eq to hope it can even attempt to check tran, not to mention being vulnerable to both magma storm and earth power, making it a shaky tran check at best.
Both are weak to shadow ball and have their stabs resisted so there is no difference in this match up.
VS: pretty equal match up, sking can neutralize the future sights with more ease but galar king cannot be poisoned. Sking does better against slack off less galar king due to bulk and water stab support but i don't know how relevant that set is.
VS: Obviously galar king is better here but did you know that slowking can avoid the 2hko from tbolt after rocks and thus can check koko?
252 SpA Tapu Koko Thunderbolt vs. 252 HP / 224+ SpD Assault Vest Slowking in Electric Terrain: 144-170 (36.5 - 43.1%) -- guaranteed 3HKO after Stealth Rock
0 Atk Slowking Earthquake vs. 0 HP / 0 Def Tapu Koko: 130-154 (46.2 - 54.8%) -- 57% chance to 2HKO
Galar king is bad against zeraora and cannot stop volt switch spam so you need a backup electric check regardless meaning in practise, slowking can serve as a backup koko check and galar king's advantage in this match up is not as bad as it sounds.
VS: Both checks np+ knock off equally but against pivot variants, slowking is slightly more vulnerable due to being weak to u-turn. Not that noticeable though cuz the damage is low regardless.
0- Atk Tornadus-Therian U-turn vs. 252 HP / 32 Def Slowking: 106-126 (26.9 - 31.9%) -- 56.5% chance to 3HKO after Stealth Rock
VS: Lele actually has a chance to ohko galar king with psyshock after rocks, making it a bad check at best. On the other hand, slowking is only 3shotted by psyshock after rocks. Even when worn down, this allows it to pivot to a resist regardless of lele's move choice.
VS: If you need help against it, then it's cm. If it's cm, galar king can't beat it with sludge bomb. Relatively equal match up.
VS: Not a relevant special attacker imo but i will mention regardless. Galarking slightly better but look at this
+2 252 SpA Ninetales-Alola Freeze-Dry vs. 252 HP / 224+ SpD Assault Vest Slowking: 152-182 (38.5 - 46.1%) -- guaranteed 3hko
Without rocks (which is not difficult because hail doesn't like rocks on it's side so it will be focusing on defogging), slowking can easily check it with flamethrower and is actually better against blizzard variants.
VS: Galar king noticeably better here. Still, slowking is only 2koed 16% of the time from full with specs modest freeze dry so it can pivot against it a couple times due to shrugging off all the other moves. Even with rocks, sking is only barely 2koed and perhaps the opponent will be forced to defog away the rocks to protect his own kyurem. Besides even galar king has a chance to get 2koed by specs modest earth power after rocks.
SubKyurem can only do about 3-5% more damage to slowking with freeze dry than it can do to galar king with earth power so not much difference there. If you run a move that breaks the sub (like psychic or power gem in case you're running scald), the matchup is fairly equal for both variants.
VS: This thing is more of a steel trapper than a special attacker so i don't think it is very relevant. Besides without specs, even modest magnezone can only 3ko king with rocks, meaning with regen support it can check zone with ease using eq.
VS: Roasts both but galar king can better fish poison.
VS: Despite the bug weakness, king is better here. Galar king is easily set up on by roost volc and cannot beat 3 attacks volc 1v1 so it is not a volc check. On the other hand, B buzz volcarona is quite rare these days and ditched in favor of psychic, roost, giga drain or safeguard. Aqua tail sking usually 2koes all volc sets, stone walls all non bbuzz variants while still tanking 1 max spa +1 bug buzz.
VS: Both are 2koed by shadow ball but kanto king can pivot in on fire moves and 2ko it back.
VS: Slowking hard walls it, galar king loses.
VS: Slowking much better cuz galar king gets 2shotted by steam eruption in rain.
VS: Galar king is much better against it but offensive variants are rare.
VS: Both fucked by specs shadow ball.
So in terms of special threats, king is better against heatran, lele, volcanion, nidoking and volc whereas galar king is better against koko, kyurem, zone and zapdos. Not quite noticeable wouldn't you say?
Maybe then the difference is against physical threats?
Physical attackers king checks: None, maybe urshifu with about 120 def evs but not going to mention.
Physical attackers king does better against:
Physical attackers galar king checks:(Not exactly super relevant offensive threats, the more dangerous knock sciz blows away galar king and bulu is rare)
Physical attackers galar does better against:
I haven't even mentioned the telesight set yet. It is quite outdated and doesn't work well in the current meta, but still gives king something else it can do.
From the matchups, it can be argued galar king is slightly better but not exactly noticeable and sking can still do it's av special tanking future sight support job well. Why exactly is then galar king a+ while slowking is being nominated to be dropped all the way to the b/ b- rank? Now, I do realize that team compositions might favor galar king (for instance urshifu pairs better with galar king than slowking) but when looking at the actual matchups, slowking is more than capable of competing with galar king so i feel it can stay at it's current a- rank.