There is a difference between informed guesses on what will happen and pure speculation for the sake of it. For instance, we can make an informed guess that Clefable will lose Softboiled, as it was a transfer move only for several generations. We can make an informed guess that Clefable will not have Softboiled.
Alolan Ninetales has Hail and Aurora Veil in thw previous two generations, and neither of these have been removed (albeit Hail -> Snow). Assuming that Alolan Ninetales will have those two traits, and thus may have Overused viability is an informed guess.
Saying that a Pokemon will get a brand new ability and randomly different stats is unserious speculation.
Here is an informed guess versus arbitrary speculation:
-The new announced type comes alongside a screenshot with Tera Blast, which is Neutral on the opposing Dragonite. Scarlet and Violet updates Tera Blast's UI to be "Super-Effective" when the Terastilize button is pressed. Therefore, Tera Blast must be neutral, and very likely is not something like "Automatically changes type to be Super-Effective." Perhaps this means this new type is more regarding neutrality than getting an advantage.
-Because the Legend Plate exists in Legends Arceus, maybe this type allows you change STAB every turn to hit super effectively?
Regardless, this all effects the Overused Metagame, Underused Metagame, Rarelyused... These changes, the DLC, effects all of them. This is not a new generation incoming, it is an update to what we are playing.