the winter walker, and presumably any other environs themed subclasses isn't directly designed to make you better in an arctic environment, it instead more took the angle of having learnt from it gave you features themed off of harnessing cold and ice, your weapon attacks deal additional cold damage, an expanded spell list of cold-themed spells, ect, ect...
in this way their themed abilities become more universally useful, a swamp ranger might excel in inflicting sickness or could have their own personal swarm to command like swarmkeeper (lots of insects in the swamp), a mountain ranger would be an expert climber and could know how to reshape stone with geokinesis and direct the winds how to blow.
it's like, yes, you could design a dragon slayer ranger to purely only have traits that activate against dragons OR you could have this ranger having learnt from their target, becoming more dragonlike in themselves, flight, to match them in their air, intimidation, you've stood strong against the king of reptiles and are considered as scary as they are, speaking draconic, learning the tongue of your enemies to understand what was previously eluded from your understanding.