Oops.
Anyways, I wanted to at least save my point about Slowking. Slowking has risen from a sleeper pick to a legit force in the meta, and I would argue the regular Slowking is actually in a better position right now than its Slowbrother. Slowbro has traditionally been better by virtue of its physically defensive prowess, but it actually has a rather unimpressive matchup against most of the physical powerhouses of OU right now. Rillaboom tears through it like butter, Bisharp 2HKOs
before SD, Lando, Excadrill and Garchomp smack it hard with EQ at +2 (Chomp can't even be 2HKOed by Scald), it can't safely come in against Kartana or Zeraora, Melmetal clobbers it if Banded, and while Hawlucha can't break it, it's always paired with a Tapu or Rilla, so Bro can be easily weakened before Lucha even comes out. Besides Lucha, the only physical threats that consistently struggle against Bro are Urshifu and Dragonite; everything else has at least one option that breaks Bro. Since both of the Slow twins struggle against most of the physical meta, it's simply more logical to use the one that at least has some staying power against the special attackers.
The other factor compared to Bro is the list of other defensive staples; overall, there are more physical walls/semi-walls than there are special ones, meaning that King inherently faces less competition for its role. Looking at the current sets in terms of dominant defensive stat:
Physically Defensive: Clefable, Corviknight, Ferrothorn, defensive Garchomp, Hippowdon, defensive Lando, Mandibuzz, non-Band Melmetal*, Pelipper, Skarmory, Toxapex, defensive Zapdos
Specially Defensive: Blissey, defensive Heatran, Swampert, defensive Fini, Tyranitar
*Melmetal invests more in SpD but its Def is still higher before items.
These mons aren't in direct competition with each other (not trying to say they are), but as a whole special wall/specially defensive isn't as crowded a market as the physical side right now and Blissey is the only other one with reliable recovery. Since a bunch of physDef mons listed have a better matchup than Bro against the current meta, I'd say you're generally better building one of those + King. Also Pex is usually physDef, and you want to compete with Pex as little as possible. Bro definitely has its place, but I'd say King generally slots in a lot easier right now.
I'd like to Introduce a new Echo fighter..
The one cost of running Slowking is it means you can't run Glowking; that said, I would argue that both Kings are really good in the meta and both have their place. The difference of Teleport means these two are naturally inclined to take on subtly but significantly different functions, as lacking Teleport means Glowking is better at running the sinister RegenVest combo, which alongside a Toxic immunity is enough to make up for its inability to pivot. Basically, it's a matter of which perks appeal to your team more:
Slowking
-Teleport
-Not weak to EQ
-Can recover without switching (since its not running AV)
Glowking
-Not weak to VoltTurn
-Toxic immunity
-More offensive pressure
-Poison- fishing with Sludge Bomb
There are certain situations where one King is definitively superior; Slow pairs better with Ferro since they cover each others weakness really well (plus Ferro can punish U-turn), and Glow pairs better with Corv and Skarm since it doesn't require a third slot for an Electric immunity. Overall, however, I would argue that both are great meta picks and both are looking to potentially get even better. Unless some big shift unexpectedly happens (and knowing my predictions, it probably will).