r.e. Gothitelle
I can't speak to 2025 tours usage since that data wasn't ever compiled, but Gothitelle's usage doesn't seem to be rising consistently in the tournament scene based on the data I have access to. While data was never compiled for the 2025 circuit, Gothitelle's usage in 2024 ranged from 10.94% (DPL) to 19.35% (SMPL), and based on Yoda2798's selected usage for the year it saw 13.76% usage, or 12.89% overall usage. Coincidentally, I recently compiled usage data for this year's SM Cup, and in that tournament, Gothitelle saw 15.38% usage. That's above its 2024 average, but still below its peak that year in SMPL. Its usage was also lower when reducing the scope to top 16, where it saw only 12.24% usage. The one tour I could find compiled usage for in 2025 was DPL, where Gothitelle saw 9.68% usage - below both its 2024 average and its usage in this year's SM Cup. All of this to say, Gothitelle's usage doesn't seem to be trending significantly in any particular direction over the past few years.
SM DOU hasn't had any tiering action since it was the current gen, so there isn't much precedent for how something like this would proceed. I think variationonatheme expressed my exact thoughts regarding potential action pretty well. I'm not particularly opposed to a suspect test, but I would be frustrated if a major change in the metagame happened based on an executive decision by the council.
If Gothitelle were to be banned, I could see the diversity of teams in the metagame decreasing noticeably. In the latest SM Cup, the meta was defined by Rain, Fullroom, and Tailwind Offense. Semiroom teams saw surprisingly little use, and niche archetypes such as Psyspam mostly stayed in their lane; Excadrill Sand didn't even see a single appearance. Fullroom and Tailwind Offense themselves have become highly centralized as archetypes, with nearly every Fullroom appearance in modern tours being verbatim the same six Pokémon as appear on the sample team, and most modern Tailwind Offense teams deviating only slightly from the core of Tapu Fini + Volcarona + Landorus-Therian + Zeraora + Kartana + Mega. (Just look at the sample teams; this exact core appears on 2 current samples and 1 past sample, with others swapping out just one or two Pokémon, such as Volcarona for Incineroar or Landorus-Therian for Zygarde.) Rain is not nearly as centralized, and interestingly is also the only of the three to regularly feature Gothitelle. For example, the Fullroom sample team was the most used Fullroom team in this year's SM Cup, with its 11 uses making up around 2/3 of Camerupt's 16 total uses. Meanwhile, the Swampert Rain sample team's 12 uses make it the most used single team in the tournament, but also make up only about about half of Swampert's total 23 uses (and an even smaller portion of Pelipper's 40 uses). If Gothitelle were banned, it is easy to envision Rain dropping off in usage and the meta being even more dominated by just Tailwind Offense and Fullroom, which are far more "solved" team styles than Rain.
Beyond just those three archetypes, Gothitelle enables several other Pokémon that would likely see little usage if it was banned. Mega Scizor (bias) really benefits from the combination of Shadow Tag giving it setup opportunities while protecting it from Intimidate and Trick Room synergizing well with its awkward speed tier and access to priority. Without Gothitelle, it would be hard to ever justify using Mega Scizor over Mega Metagross, which is already a dominant presence in the metagame. Mega Manectric is another example of a Pokémon that would fall off significantly without Gothitelle. Manectric's main strength is the combination of fast pivoting and Intimidate, but it can struggle to leave an impact when it's easy for the opponent to simply switch around its debuffs. Without Gothitelle, Manectric would be far more niche, needing hazards to function but also wanting Defog to enable its own constant pivoting in the face of opposing hazards, two team elements which generally do not mix. Then there are even more niche examples like Persian-Alola, which provides value mainly through Parting Shot; its rare appearances are often supported by Gothitelle. Slower attackers without their own speed control would likely drop slightly in usage, especially as the more traditional semiroom TR setters (Cresselia, Diancie, and Mega Gardevoir) are in a bit of a rut. (Though Cresselia in particular may swing back to some degree if Gothitelle is banned, as it does more directly compete with Gothitelle than the other two.) Some minor archetypes, such as Intimidate / debuff spam and Rain semiroom, are likely to significantly fall off as a whole without Gothitelle.
Finally, I just want to throw this out there - if Gothitelle is banned, I think the logical next consideration is whether Snorlax should be re-tested. The consensus at the time of Snorlax's suspect test was that it was mostly being tested and considered broken because of how powerful the Gothitelle + Snorlax core was, often also with Manectric-Mega. Now this isn't me saying I think Snorlax would be completely fine in a metagame without Gothitelle; I don't feel I am educated enough on the subject of Snorlax in Gen 7 DOU to have an opinion on the matter.
TLDR: Based on the data I have access to, Gothitelle's usage does not seem to be consistently rising in tours. I believe banning Gothitelle would reduce metagame diversity by centralizing the meta further around the highly optimized Tailwind Offense and Fullroom structures, and by indirectly nerfing several niche Pokémon. If Gothitelle is banned, I believe Snorlax should be at least considered for a re-test, as Gothitelle played a significant part in its ban. Most importantly, I think it's important that, if action is taken, it is done via suspect test or with community input in some form rather than via executive decision.
