Its an argument in the sense its unproductive and does nothing for us. Breaking precedent for the sake of lower tiers (which is unprecedented in itself) means nothing gained. Hypothetically speaking whether that it does nothing or something for the tier.
I appreciate the more in-depth explanation and will admit I overlooked some of the major differences when making my case, its not 1:1 sure but I still think we're using tera button as a balance lever in this case. I would've argued terapagos getting defensive / offensive boost from its form swap is not that different in practice (in a tunneled 1v1 scenario where a setup sweeper just needs to brute force or tank something) from the type changing of tera as a mechanic / additional STAB / increase in a primary STAB or reduce the effectiveness of a would be revenge killer / offensive matchup trying to eliminate the threat before it gets going, but I now understand the more limited pool its working with.
Either way I'm not sure how you setup a clause for specifically targeting 1 tera type and not just roll with that on other tera users. Mega ray spawned a whole format of its own to serve as its banlist since the original banlist (ubers) wasn't playable with it around, I don't think terapagos compares cause its just sharing a trait everything else is using, mega ray doesn't require its item to use its mega and dragon ascent for whatever could use it (base ray and.. smeargle?) wasn't the problem so there's no physical element to lock out of the tier. Terapagos you can't lock out stellar off the premise that stellar is fine on literally everything else, and there is no item associated (mega stones). You're just disabling the mechanic for specifically this 1 pokemon cause it has a special interaction after its used, this could've been done for a lot of pokemon including in the past enabling individual gigantimaxes that sucked compared to average dynamaxes as a whole cause 'gigantimaxes were special case form swaps' (would kingler but broken in OU if you can enable a would-be globally accessible button for specifically it if gigantimax was its only option? Doesn't mean you need to free RNG shit like butterfree but it means you can discuss who or what gets privileges to a generational mechanic.), the button was disabled for all.
FWIW the mega ray case was in itself a huge mess and probably could've been handled better, that was a knee-jerk reaction to how comically broken it was at the time and the process wasn't as thought as out beyond 'just getting rid of it'.
Just don't see a real approach for Terapagos + stellar ban cause you could result in the pretext that stellar breaks the mon; why not just ban tera fairy + moon/volc atp, or chi-yu + STAB tera to nerf its damage? If its not a specific tera cause that tera doesn't break anything else and you're disabling the button for specifically terapagos then why not just disable the button on the tier's most egregious users?
I feel like there's a misunderstanding going on with Terapagos again based on the way you're arguing against its ban as "Terapagos + Stellar" or Stellar being fine on everything else. Understandable since Terapagos hasn't been playable very long in any relevant OU format (and is irrelevant in Ubers so not likely to experience much there either), but it's another distinction that brings us back to arguing from a flawed premise, much less questionable arguments to support the example.
Terapagos-Stellar is not necessarily the same as a hypothetical "Terapagos with a Stellar Tera Type" like Roaring Moon with a Fairy Tera type. Terapagos's Stellar form is a flat out new Pokemon form by most relevant metrics (Stat changes, a signature move interaction, and being hard-locked into its own version). You do not have the option to play Terapagos with the standard version of Tera (i.e. Terapagos-Terastal with a Fire, Water, Fairy or even Stellar Tera type and no non-generic interactions). This is one respect in which Terapagos-Stellar functions closer to a Mega than a standard Terastalization (and why I think I at one point off-handedly mentioned Ultra Necrozma being to Z-moves a similar edge case). It is to the point that the Orange Islands threads hacking Terapagos to use other Tera types STILL turned into the Stellar form with the Stat and HP increases, and Tera Starstorm seemed to retain its behavior (Tera Ghost was hitting Normal and Ghost targets for regular damage, and Terastalized claimed "Super Effective"), all of which mark that Terapagos-Stellar is coded as a distinct Mon/Form in the code rather than simply a modification on top of Terapagos-Terastal as most standard Terastalizations or theoretically Dynamaxes were. Gigantamax is again a non-starter because it doesn't actually alter NEARLY as much about the user's gameplay compared to standard Dynamax as compared to Terapagos-Stellar vs standard Terastalization: you still retain traits that made it unbalanced such as on-demand triggering of 2x HP, the majority of generic Max moves and their corresponding secondary effects, and immunity to several interrupt mechanics. This analogy would only maybe work if Terapagos had regular Tera access and changed ONLY Tera Starstorm on Terastalizing, bringing it much more in-line with the function of other Terastal users, but in that scenario it would not be a stand out edge case that warranted this talk of Policy vs a Standard suspect in the first place.
ETA: Something else I learned is that Ditto is capable of turning into Terapagos-Terastal, but it cannot become Terapagos-Stellar through any means, be it trying to directly Transform, or turning into Terapagos-T and then Terastalizing itself (Stellar or otherwise). Notably, Ditto is capable of Terastalizing after transforming into any other non-Unique-Terastal Pokemon (i.e. Ogerpon forms) using its own Tera type, but once Ditto is Tera-Stellar'd specifically, Transform fails on subsequent uses (such as if Ditto leaves and comes back): the important interaction here is that Terapagos is the only (relevant to this topic) Pokemon that does not let a Transform Pokemon Tera AT ALL, another indicator that Terapagos-Stellar is a separate form rather than just a Terastalized Terapagos. Transform does not allow the Transformed Pokemon to form change in-battle from the Transformed state (as pertains to things such as Minior's Shields Down, Aegislash's Stance Change, etc), and several forms do not allow Transforming directly into them, usually they default to a regular state (such as Dynamax becoming the normal version) or blocking the Transformation explicitly as we have now. Just more fuel on the point being clarified
It is NOT sharing a trait everything else is using unless you are strictly referring to the 1-click Tera Button as the resource expended, you cannot in anyway produce a comparable "Kingambit-Stellar" with comparable changes to its stats or unique mechanical behaviors. This isn't "Terapagos + Stellar" ban, this is "Terapagos-Stellar as a specific form" in concept, it's not a complex clause in terms of phrasing or understand in its own case, and at least personally I'm not convinced of any slippery slope it opens the door for when we have precedent for tiering player-triggered-in-battle forms separately with Megas. Rayquaza only specifies the precedent for banning the Mega directly rather than a roundabout method that accomplishes the same like "Stone is banned, stone only matters for Mega Evolution anyway." Slippery slope of disabling the button "the tier's most egregious users" is a non-start because they use the button exactly the same as everything else, and are not inherently overpowered to a quickban degree when using the Terastal for the team; neither of these statements is true of Terapagos, with Terapagos-S being a very unique and specific transformation off the mechanic, and Terapagos-S being FAR more egregious and unhealthy than anything currently in OU or even being discussed for drop like Roaring Moon. The button being disabled is because it offers Terapagos exactly 1 option, is easily replicable on Software with our usual ruleset practices, that option is the one thing that makes it egregious, and the button enables a different form entirely rather than simply an addition to a kit that is fundamentally the same Pokemon otherwise. This also distinguishes it from something like Archaludon or Annihilape signature move talk, because Terapagos-S is a different Pokemon in multiple functional ways, rather than one piece of a kit that is considered unbalanced only when viewed holistically.
