Natural history enthusiast
So who exactly "recognizes" these brands as alphas or not? Who are these people?
Just like the meaning of any word, it is defined by prevailing practice of the community of users. The birding (or birding+optics) community is most relevant here. Swarovski and Zeiss get no argument as alphas. No one ever has to defend them, ergo they are alphas. Leica is very much a prestige brand in the world as a whole but may be slipping a bit within our community when it comes to products that impress; still, it's very much an alpha brand. Nikon is always the add-on, is frequently defended as an alpha, and therefore isn't.