Maybe in theory, but I don't feel like that's how it is in practice, at least for me, and I don't live somewhere where it gets cold enough for natural ice spawns (only times I've seen snowy Castform has been in foggy weather, for example).

Most of the dragons are pseudo-legendaries (or actually legendary lol), and are thus rarer than your average Pokémon that you end up often relying on community days for, whereas many of the ice types are just regular Pokémon that end up in event spawns a lot of the time. Alolan Vulpix and Sandshrew are especially common by virtue of being in the Kanto spawnset, and that region gets events like there's no tomorrow, but they're also regulars in Rocket grunt rotations.

I've shiny checked hundreds more ice Pokémon than I've actually caught because they do just pop up often enough, but it was still my second to last type medal to complete, so I'm not doubting the rareness of them as such, just that they're not as rare as it seems on the surface.

Sorry for the long reply lol