In order to make a fully informed decision on whether Throh is banworthy or not, I think the voters in this suspect should first examine two key factors as they enter this debate: firstly, is Throh considered to be broken in this current metagame? What sort of counter-play does the opponent have for Throh that would prevent it from being broken? And secondly, would the re-introduction of Throh be healthy for the tier, in that it helps balance each style of play (i.e. Offense, Balance, and Stall in a nutshell)? Along this same line of thought, what are Throh's effects on teambuilding - does it ease teambuilding on the whole and add something that the tier needs, or is it over-centralizing to the point that each team must contain a Pokemon geared toward beating Throh? I think that a lot of the arguments stated before this post have been somewhat incomplete on the whole, as they fail to consider both halves of this basic tiering philosophy; they either state that, 'no, Throh isn't broken, so unban it,' or 'yes, it's clearly threatening to defensive styles of play, so keep it banned.' So, to avoid these sorts of one-sided thought processes that tend to encourage bandwagoning, I'll touch on both questions in this post, as they are equally important when considering whether or not a Pokemon should be removed from a tier.
Firstly, it'd be unlikely for me to ever argue that Throh is broken in the context of PU, especially because it's being re-introduced into a fast-paced, predominantly offensive metagame that is rife with threats which have the capacity to OHKO Throh (or at the very least, revenge kill it from higher HP percentages). For example, the recent popularization of Pokemon like LO Murkrow, Colbur Grumpig, Specs Mime, LO Kadabra, CB Ninjask, and offensive Pelipper, or even older sets like Jumpluff, CB Dodrio, Arbok, Swanna, and Articuno mean that most offensive teams will have at least one check ready to revenge kill Throh. What's more is that its horrible Speed stat (uninvested base 45 - or 126 Speed total) leaves it liable to be revenge killed by a plethora of faster Pokemon, given most of PU is in a higher Speed tier.
Additionally, the presence of new drops have also hampered Throh's effectiveness for the most part. While it takes a lot of damage if Throh is healthy (i.e. above 74%), CB Bouffalant can OHKO Throh:
252+ Atk Choice Band Bouffalant Return vs. 192 HP / 32 Def Throh: 270-318 (62.9 - 74.1%) -- guaranteed 2HKO after Leftovers recovery
252+ Atk Choice Band Reckless Bouffalant Head Charge vs. 192 HP / 32 Def Throh: 379-447 (88.3 - 104.1%) -- 31.3% chance to OHKO
Another more obvious example is Exeggutor. Colbur Harvest Exeggutor can switch into SleepTalk variants without fear and either force Throh out or do upwards of 80-90% with Psychic STAB while it eats up hits from Knock Off:
252+ Atk Throh Knock Off (97.5 BP) vs. 72 HP / 0 Def Colbur Berry Exeggutor: 111-131 (31.8 - 37.5%) -- 89.3% chance to 3HKO
252+ SpA Exeggutor Psychic vs. 192 HP / 32 SpD Throh: 348-410 (81.1 - 95.5%) -- guaranteed 2HKO after Leftovers recovery
252+ SpA Exeggutor Psyshock vs. 192 HP / 32 Def Throh: 308-366 (71.7 - 85.3%) -- guaranteed 2HKO after Leftovers recovery
Gorebyss, if healthy, can also use Throh as setup fodder if you know Throh is carrying Storm Throw over Circle Throw, which is actually quite common on more offensive teams:
252+ Atk Throh Storm Throw vs. 0 HP / 0 Def Gorebyss on a critical hit: 130-154 (51.7 - 61.3%) -- guaranteed 2HKO
+2 252+ SpA Gorebyss Hydro Pump vs. 192 HP / 32 SpD Throh: 397-468 (92.5 - 109%) -- 56.3% chance to OHKO
+2 252+ SpA Life Orb Gorebyss Hydro Pump vs. 192 HP / 32 SpD Throh: 516-608 (120.2 - 141.7%) -- guaranteed OHKO
Even Gothitelle's CM set is able to bypass Throh; with just 96 SpA and no CM boosts, Gothitelle is able to 2HKO Throh with Psychic with Leftovers factored in:
96 SpA Gothitelle Psychic vs. 192 HP / 32 SpD Throh: 228-270 (53.1 - 62.9%) -- guaranteed 2HKO after Leftovers recovery
With all these factors considered, I would find a situation in which a newer player beats a more experienced one just because the newer player is using Throh to be extremely unlikely. In other words, Throh should not be considered broken because our meta has already made the necessary accommodations for Throh: it has enough checks to prevent it from being broken, it is easy to revenge kill with its horrible Speed, its RestTalk set is easy to outplay with moves like Encore and Taunt, and it has fairly reliable options for counterplay in Pokemon such as Colbur Harvest Exeggutor and Jumpluff, to name two examples from the list I gave above.
Now that I've touched on why I don't think Throh is broken, I'll talk about its effects on teambuilding and on the tier in general:
I'll argue that Throh actually eases teambuilding - in my experience, there have been defensively oriented teams that I've tried to build where I absolutely needed something for Knock Off absorption as I was using Eviolite-dependent options like Roselia. At the same time, I needed the resistances a Fighting-type would provide, along with the ability to phaze in order to take advantage of entry hazards. In the past, I would have used Poliwrath for such a role, but since its rise to NU, Machoke never quite had this same ability to act as a Knock Off absorber, phazer, bulky Fighting-type, and, without being dependent on Eviolite, to act as a blanket check to offensive Pokemon. So, while it can't be stated enough that Throh is a huge threat to defensive teams, its presence is actually helpful for building Stall itself because of its ability to beat huge threats to Stall, such as Vigoroth and Pawniard, while providing the utility I mentioned.
In addition to beating these stallbreakers handedly, Throh also acts as a balancing presence when viewed under the lens that fast and frail offensive Pokemon are dominant in PU. For example, Zebstrika is used quite often in this meta for its ability to check Floatzel fairly reliably, and its presence in the top of A+ in VR is proof of my statement that PU is a predominantly offensive metagame. However, the re-introduction of Throh provides PU with an answer to Pokemon similar to Zebstrika, in that they are unable to OHKO (or even 2HKO Throh, in Zebstrika's case), while Throh can survive a hit with ease and strike back with a Storm Throw that does up to 80%, or it forces Zebstrika to Volt Switch out as Throh finds an opportunity to use Rest.
252 SpA Life Orb Zebstrika Thunderbolt vs. 192 HP / 32 SpD Throh: 153-181 (35.6 - 42.1%) -- 88.8% chance to 3HKO after Leftovers recovery
252 SpA Life Orb Zebstrika Volt Switch vs. 192 HP / 32 SpD Throh: 121-142 (28.2 - 33.1%) -- 87.3% chance to 4HKO after Leftovers recovery
Floatzel finds itself in a similar position to Zebstrika. At best, its Specs boosted Hydro Pump is a 2HKO (not including its chances to miss), while Banded Waterfall is a 3HKO with Throh's Leftovers factored in:
252 Atk Choice Band Floatzel Waterfall vs. 192 HP / 32 Def Throh: 186-220 (43.3 - 51.2%) -- guaranteed 3HKO after Leftovers recovery
252 SpA Choice Specs Floatzel Hydro Pump vs. 192 HP / 32 SpD Throh: 223-264 (51.9 - 61.5%) -- 96.9% chance to 2HKO after Leftovers recovery
These examples of Throh putting faster, offensive teams in tight spots via its high bulk are numerous. Most of the time, if Throh is healthy, it finds itself in a position to either force a switch on something frail like Raichu, Zebstrika, or Floatzel, or it is able to take a hit and OHKO in return after SR damage. In other words, what I see happening generally is that the mere existence of Throh is often enough to threaten offensively based teams if they do not possess a Pokemon that has something to check Throh (i.e. Psychic or Flying STAB, most of the time). This could be enough to slow down our overly offensive metagame to the point that slower wallbreakers could gain popularity again, lending viability to other, somewhat slower and bulkier teams on the whole. This, in conjunction with the fact that Throh is able to beat Stallbreakers like Vigoroth and Pawniard, says to me its presence could be balancing to the meta in the longterm.
With everything considered, I am currently leaning toward it staying because I do not think it's broken thanks to its low Speed, its ample number of checks, opportunities for counterplay when facing Throh, along with the idea that its overall effect on teambuilding is positive and that the meta has already adapted to threats like Machoke and Monferno, making Throh much more balanced than when it was here earlier this year.