My main gripe with Dugtrio's ranking currently is that it cannot really be compared to anything whatsoever. And while I understand that we shouldn't really discuss it much, I wholeheartedly disagree with a lack of discussion regarding what is easily the most controversial mon in today's OU.
One of the earlier posts stated that Dugtrio has a great influence on the metagame but that the likes of Tapu Bulu, Volcarona, and Zygarde do too. My main problem with this statement is that, unlike those three, Dugtrio has no competition for its role. Z-Move Garchomp is also an effective wallbreaker, although it lacks the sheer nuking ability Bulu has. Volcarona performs its special sweeping role a bit better than the likes of Autotomize Celesteela (although this thing's admittedly fallen from grace lately) or other special nukes incapable of boosting up like Volc can. Zygarde has its bulk and versatility going for it but the role of a Dragon Dancer still happens to be shared by Mega TTar, which is quite prominent in today's metagame, and Zard X, which is far less common but still has its niche. Nothing, however, can revenge kill a wide variety of threats to nearly the extent Dugtrio can while having the ability to remove any counterplay to it.
To quote the NU Viability Rankings this gen (before anyone says anything, I'm immediately assuming the same mindset goes into deciding this tier's rankings):
"(To make ranking these Pokemon easier the NU Council has come up with a list of positive and negative attributes each Pokemon should meet to fit a certain rank.) Positives: Threat level, Splashability, Consistent, Effect on the metagame, Reliability. Negatives: Passive, Outclassed, Weak to Hazards, Speed, General Bulk, Matchup.
"S Rank:
Pokemon in this rank fill all of the main criteria and then some with a strong proficiency in one or more of the positive traits. If a Pokemon in this rank has any downsides, they are usually tame or eclipsed by their obvious assets."
To go through each point, one by one:
Threat Level: Huge. Dugtrio is able to revenge kill a gigantic portion of the metagame with one of its many set/item options. Dugtrio has no counters by definition of a counter, as nothing bar anything with a Shed Shell, Levitate, or Flying/Ghost-types can switch out. Due to having such limited counterplay and having the ability to trap and revenge kill anything, even if the opponent makes numerous correct predictions and eliminates something by making such a good play, Dugtrio is easily one of the biggest threats in the OU tier.
Splashability: Very good. It is almost mandatory to run on typical Stall teams. Even more situational Stall teams, like some VinCune teams outside of Veil, strongly appreciate Dugtrio's ability to remove powerful and fast Electric-types, like Tapu Koko, that would severely hinder Suicune's ability to stall or sweep teams. In addition to being a Stall staple, it finds its home on more offensively-inclined teams. It forms a devastating offensive core alongside Zard-Y and Tyranitar because of its ability to seamlessly trap and eliminate the likes of Chansey and Toxapex. Said core is among the best and most consistent in the metagame. I would hardly say the likes of Landorus-T and Magearna are literally mandatory for a certain playstyle on top of being excellent for some others.
Consistency: It requires half a brain to use, but depending on the item you opt to run (Focus Sash, Choice Scarf, Groundium Z) you're only using Dugtrio to trap and eliminate specific threats. It will always be able to beat the likes of Heatran, regardless of its set. Assault Vest Magearna is always OHKOed by Tectonic Rage. Chansey always loses to a healthy variant of the same Groundium-Z set. Volcarona requires less than 20% prior damage to be consistently OHKOed by the Choice Scarf variant's Stone Edge, through its Charti Berry. Dugtrio exists to remove specific threats from OU but nothing in the metagame can perform that role quite as well.
Effect on the Metagame: Dugtrio's very existence threatens numerous OU-viable threats. Teambuilding with it in mind is very difficult because it has no real counterplay. When Dugtrio appears on the Team Preview the game becomes more a war of prediction and attrition because Dugtrio can punish a single bad play by trapping and removing a mon, potentially breaking a powerful core. In addition, Dugtrio's trapping abilities allow it to punish
good plays, too. The threat of having your Heatran removed from the game even if you manage to get a really good prediction on your opponent and OHKO something,
or even if you just get a crit you didn't account for that would've been awesome under any other circumstances, is ever-present. Unlike Magearna and Landorus-T, which are incredibly versatile, Dugtrio only has three-odd variations of its exact role but that role is extremely fearsome to the point where you have to play the game completely differently when there's a Dugtrio on your opponent's team.
Reliability: Again, Dugtrio exists to trap and eliminate specific threats. It's incredibly reliable in that it is the
best at beating those threats more often than not. Dugtrio is, for the most part, only used to eliminate those threats, and then it can usually end its hot streak by crippling a wall with Toxic or sacrificing itself with Memento in order to let a setup sweeper come in and wreak havoc for the rest of the battle.
Passiveness (or lack thereof): While Dugtrio isn't really doing much to Landorus-T, Tapu Bulu, or Celesteela early in its life, Dugtrio is by no means passive. It can break past Chansey, OHKO Volcarona with Stone Edge through the Charti Berry after only a minor amount of prior damage, irreparably damage even AV variants of Magearna, and much, much more. Dugtrio is only quite passive against things it's not supposed to come in on anyway.
Outclassed?: As I mentioned earlier on, absolutely not. Nothing performs Dugtrio's role except for Diglett (don't use this) and Trapinch (don't use this). Both got their fair share of usage during the Dugtrio suspect. But as long as Dugtrio is used in OU, nothing comes even remotely close to performing its role in the tier. Dugtrio is incredibly unique, and cannot be outclassed in its current state.
Hazard Weakness: This is a bit more relevant to Focus Sash variants, admittedly. Other variants don't care much for any chip damage from hazards since Dugtrio is incredibly frail. If it means anything, it packs a Stealth Rock resistance.
Speed: Base 120 Speed is nothing to scoff at. For a Groundium-Z wallbreaker it's an incredible speed tier. Because its role is as influential as it is it can run a Choice Scarf to reliably outspeed the few OU-viable threats that can outspeed other variants. Tapu Koko and Mega Manectric can't beat it 1v1 all of a sudden. Greninja takes up to 79% before hazards and LO recoil. Tornadus-T takes colossal damage from Stone Edge after rocks (LO variants are almost always OHKOed). Mega Alakazam can get trapped by Pursuit or can die to Earthquake after just a tiny bit of chip damage (25% chance to be OHKOed from full after rocks).
Bulk: Dugtrio doesn't really have any bulk. It dies to almost any hit that doesn't do fixed damage like Chansey's Seismic Toss. Largely the reason why it doesn't really care about hazards too much. That being said, it more than makes up for its lack of bulk by being able to trap and OHKO numerous top-tier threats. If it's taking a hit it either did its job already or wasn't used correctly.
Matchups: Dugtrio picks its own matchups. Much like Shadow Tag during a much darker era, Dugtrio's Arena Trap means that it is, more often than not, dealing with the opponent on its terms. When it's in an unfavorable matchup it's more often than not paired with something that can switch in, or it simply uses Toxic or Memento and has lasting effects on the outcome of a match even after it's dead.
So given all this - assuming these are the qualities that determine a mon's viability in any tier (I can't see why those criteria wouldn't apply here, honestly) - why is discussion for Dugtrio's potential in S so discouraged? Unless I'm missing something it has many of the qualities to push it above and beyond the threats in A+.