I mean the first time we ever see a Gore Magala on-screen is in the Intro Movie before the game starts where it literally One-Shots a Tigrex so it's very clearly shown to be superior to Apex Monsters and Seregios still has those statements and feat going for it.
While that intro movie was impressive, stuff like that happens in cutscenes all the time to show how threatening an introduced monster is.
In its Rise cutscene, Diablos
completely and unquestionably defeats both Anjanath and Barroth at the same time with a single hit, while it's
shown to tie with Anjanath in turf wars later on. It, too, took them by surprise in the cutscene, but turns out to actually be comparable with Anjanath in reality.
By the same metric, Ebony Odogaron
kills an Odogaron by the exact same method Gore kills Tigrex - by snapping the neck, yet it is still considered to be a monster on the same level. Arguably, since Odogaron fought back and still got stomped while a wounded Tigrex was jumped with no chance to do anything in response before its neck was crushed, I'd say Ebony's showing is more impressive than Gore's due to no-selling and overpowering literally all of its opponent's attacks.
I think it's perfectly reasonable for a monster that's relatively in the same league as another to win by putting it in an extremely compromising position entirely by surprise and using that advantage to snap its neck, rather than necessarily having to be 820 million times more powerful. We even see with Gore's Ecology in Sunbreak that its wing arms are incredibly strong for its size, able to
overcome a Goss Harag (granted, one that was already on its back) who previously broke from its regular claw grip, so yeah, I'd see that breaking a neck if it was able to surprise a monster with a relatively long neck as Tigrex. If we do get a Gore vs. Elder Dragon turf war, then I'd be all for it, but as of now, I don't see how Gore, and by extension Seregios, need to be in the same tier as the other Elder Dragons to do what they've been shown to do.
And again, Azure Rathalos and Barioth would have to be upgraded alongside Seregios if this goes through, considering they've clearly been able to fight one on equal terms (or even be winning) in the past. I don't think that'd fly, since then pretty much every monster stronger than a Tetsucabra would be Elder tier by these metrics.
Tbf, didn't Velkhana unironically K.O. the Sapphire Star at one point? I swear I remember that happening but it doesn't help that I was never able to get my hands on Iceborne for myself.
Oh yeah,
that scene happened. Velkhana conjures ice crystals in the air for the first time, and said crystals dropped right on the Sapphire Star's head/back of neck. It actually makes a point of showing that the crystal landed on their head, probably to justify them conking out on the spot. But yeah, Velkhana was definitely treated by the Iceborne story as something so terrible as to justify the entire Commission evacuating, with something about 'the whole New World freezing over' or something to that effect after seeing just the frozen body of a single Anjanath. I can see it as a higher form of Elder for sure. Though it ties with Kushala and Teostra in turf wars, so idk.