After reading your post, I'd like to respond with some counterpoints.
Is Tera problematic in enabling certain Pokemon? Sure; however, banning Tera would open a much worse can of orthworms and would heavily stifle the creative freedom that it enables in team building. Banning Dynamax in Gen 8 was understandable as there was generally no way to handle a mon suddenly gaining double HP and superpowered moves. Would a post-Tera meta be more balanced? It's hard to say, but it would (ESPECIALLY in the long term) make team building far more suffocating. Tera enables such a wide variety of Pokemon to be used with creative niches, and as a result, Gen 9's OU is the freshest, healthy, and most diverse that an OU meta has been in a long time.
Banning Tera isn't like banning Dynamax - Gen 8's OU arguably didn't lose its flavor and flourished as a meta because dynamax directly stifled team cores. The logic you used regarding "a big advantage on the turn a player used it" could also have been applied to Z-Moves in Gen 7 (which were arguably more broken than Tera, I still hold that view). I wholeheartedly believe that banning Tera would do nothing but kill the creative freedom Gen 9's OU offers in team building, and that the added prediction difficulty mentioned is more than justified with the precedent that Gen 7's Z-moves set in addition to the massive positive boons that Tera provides OU's landscape.
Call me a Tera simp, because I'm sure I can speak for quite a few people when I say that a tera-less Gen 9 OU would be a far more centralized and creatively stagnant meta that many would lose interest in playing all together. Imagine Gen 5 without weather wars - weather in Gen 5 is, at least in my view, at the same level as Tera (if not due to unpredictability, due to teambuilding influence and enabling specific threats), yet it's understood that banning Politoed, Ninetales, Abomasnow, etc would make for a far worse meta experience overall.
The “Greedunt has an OU niche” guy be spitting facts. Tera has led to a meta where even mons that have never had an OU niche are useable now. Luxray, Cryogonal, Golduck, Umbreon, etc. They barely reach D tier but the fact that they have a small niche in this power crept tier shows the benefits of Tera.
However Tera also has led to frustrating games with how mu fishy it is. Gambit is one of the biggest offenders of this I feel. Tusks feels obsolete as a Gambit check since all it has to do is click Tera Flying to flip the mu around. Tera Fire is a big f u to Volc and burns from Washtom. Tera Fairy is a nice middleground that also eliminates its fighting weakness. Sometimes it just sweeps games by itself.
Volcarona has always been the mu Moth it was in Gen 7. Most of the other Teras mentioned (Fire, Ground, and Psychic) aren’t incredibly common like Grass or Fairy. Volc wants GD for Garg/Washtom. Psychic for Pex and Moth. Ground Tera Blast for Skele. Morning Sun for defensive utility. Unlike the mess Espa put everyone in, its checks are reasonably splashable and doesn’t boil down to running Tera Dark on Clod. Plus there is one major answer to it that is splashable and beats non-Wisp variants. Dnite. It boosts up in its face and kills with E-Speed/EQ.
Ghold is the first mon in a longtime that warps the meta around it without being broken. It creates a dynamic akin to GSC Lax, ADV Ttar, DPP Rachi/Clef. The Cheese stick man is fine. People have gotten so comfortable with handling hazards. SS especially made hazard control trivial. Run boots and the 7 good defoggers in the tier. For the first time in 10 years you now have to think consciously about the hazard v hazard removal meta. This isn’t the first gen where hazard removal was limited, DPP OU and BW NU come to mind. They had even worse options than we do. DPP’s only used spinner was Starmie which has been declining in usage as a spinner, hence why most DPP teams choose to build teams without any removal. BW NU had garbage hazard removal, their best option was fucking Wartortle.
SS OU has
-Tusks, the #1 most splashable mon in the tier that also makes Ghold hesitate.
-Treads who has an even better mu against Ghold.
-Court Change from Cinder.
-Hatterene
-Boots, the item people complained about nonstop last gen. Also with less Knock distribution, they are less likely to lose them.
-Tons of spike immunes with Corv/Washtom/Dnite/Peli/Hydrei/Jugulis
You don’t even have to run Tusks to make a good OU team. There is a thing called Superman teams, which I covered already in this post. TL;DR, OU teams have always had teams that are built to minimize the effects of hazards without utilizing hazard removal.
https://www.smogon.com/forums/threa...-6813-new-tiering-survey.3710915/post-9478697
Ghold itself is not short of reliable checks/counters. The most notable being Gambit which is more reliable as one considering Ghold has been dropping Focus Miss for sustainability with Recover. Clod, especially Unaware Clod can check it with the exception of Tera Flying variants. Ting-Lu lives any hit and chips it down with EQ or Ruination. Moth can eat a Sball and force it out. Same with Volc. Chomp can live a hit and force it out. Dnite can shrug off a hit, DD up, and threaten with EQ. If it chooses to Tera, it just gets picked off by E-Speed. There is also the fact that non-Scarf Ghold is slow as shit. 84 speed gets it outrun and rkilled by Pult, Meow, Hydrei, Gren, etc. Terastilizing it is worthwhile but not without opportunity costs. Any Tera that isn’t Ghost means it loses the utility of being a spinblocker. It risks losing its ability to check Valiant. Tera Flying, the most common one, makes it weak to Rocks while losing the plethora of resistances. Its not the same as Tera Dark Pao which got nothing but benefits from it.
Now back to Terastilization itself. I still stand that Tera should’ve been toggled with team preview, but I don’t think the mechanic as a whole is broken….yet. Home is looking to bring in even more power creep. Some old mons that were balanced in Gen 8 may not be with tera. NP Torn with Tera, Urshifu-RS, Eleki, Volcanion, Battle Bond Gren, Zapdos, G-Molt, Hoopa-U, Tran, maybe even Lando-T. Then you got new shit like Basculegion, Sneasler, and Enamorus that will be downright devious with Tera.
252+ Atk Choice Band Adaptability Tera Water Basculegion Wave Crash vs. 252 HP / 252+ Def Rotom-Wash in Rain: 224-264 (73.6 - 86.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252+ Atk Choice Band Adaptability Tera Water Basculegion Wave Crash vs. 252 HP / 252+ Def Toxapex in Rain: 175-207 (57.5 - 68%) -- guaranteed 2HKO after Stealth Rock and Black Sludge recovery
252+ SpA Choice Specs Tera Flying Zapdos Hurricane vs. 252 HP / 232+ SpD Heatran: 135-159 (34.9 - 41.1%) -- guaranteed 3HKO after Stealth Rock and Leftovers recovery
+2 252 Atk Life Orb Tera Water Urshifu-Rapid-Strike Surging Strikes (3 hits) vs. 252 HP / 252+ Def Toxapex in Rain on a critical hit: 264-315 (86.8 - 103.6%) -- approx. 93.8% chance to OHKO after Stealth Rock
252 SpA Choice Specs Tera Water Volcanion Steam Eruption vs. 252 HP / 4 SpD Rotom-Wash: 170-200 (55.9 - 65.7%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
252 SpA Choice Specs Tera Water Volcanion Steam Eruption vs. 252 HP / 252+ SpD Slowking in Rain: 183-216 (46.4 - 54.8%) -- 64.5% chance to 2HKO
Down right devious calcs. We haven’t even gone to the defensive utility they can offer. Goltres with Tera Fairy/Steel/Ground. Torn with any Tera. Volcanion shedding its Ground/SR weakness with Tera Water. Watershifu with Tera Poison/Electric/Fairy. Right now Tera is just annoying but fun, however Home is gonna show the true chaos with allowing this mechanic in OU.