Honestly, I'm not a fan of putting Terapagos teraing and every other Pokémon as literally the same thing. Besides the name, what Terapagos does is simply not a universal mechanic. The universal mechanic of Terastalization allows you to choose any of the types available in the game, changes your type, and boosts the power of the Tera type. The universal mechanic of Terastalization does not make you change your ability, give you +100 BST, and quite literally changes you to a different forme of the Pokémon, with no option of changing what type you want. It is a unique mechanic to Terapagos that just shares the name with the others - and in a VERY relevant way, not something minor like Dynamax vs Gigantamax. Held items are also a universal mechanic of the game, but we still banned Gengar from holding Gengarite, not Gengar from holding items, Gengar, Gengarite, or Mega Evolution, or holding items in general.I don't understand the comparison between Terapagos Stellar form and Mega at all. It's called a separate form, and it gets different stats, but it's really not. It's what happens when this pokemon Terastilizes, a mechanic every other mon in the tier can do. It also is locked into that type of Tera. It can't do a "regular" Tera.
What people are arguing for is just making this mon arbitrarily be unable to Tera, a key mechanic of the gen. This isn't banning an item from that mon like with Mega evolution, this is removing the ability to do a thing every other mon can do because when this mon does it, it's broken. That doesn't make a lick of sense to me. That'd be like banning the move "protect" from a Pokemon who's exclusive ability it is to do 50% damage to the opponent every time they did protect. It's clear this mon is busted, implementing a ban to remove the use of a universal mechanic on one specific pokemon because it uses that mechnanic in a special broken way opens a huge can of worms and will damage the tiering process down the road.
If Tera as a whole gets banned, then yes, it'd make sense to bring the turtle back, but as of now, no way in hell should we entertain banning just the "stellar form" because that is a misnomer. What people are actually suggesting is locking the tera function on a specific pokemon in a meta where every other mon can tera at any time. It's sloppy, and it shouldn't be done.
I do plan on making a Policy Review thread on Terapagos-Stellar since I think the metagame discussion thread is not the best place for it - there's tons of stuff relating to the actual meta to talk about, alongside the fact that this is something the goes beyond OU and affects Smogon in general - remember, base formes weren't separated from Megas initially until ORAS where there was a Policy Review discussion, as Charizard was also attached to Mega Charizard X and Y, so base Charizard was OU and couldn't be used on lower tiers. Terapagos has similar cases for us to compare, but no one-to-one comparison, it's simply a case of its own.