If that's all it is (the purple part plus a little more where it's cut off) that's not really THAT large. For a Souls game, sure, it's big, but definitely not "incredibly huge" by any standard.
There were some theories that the map was actually the ring in the game's title, as in what we've seen so far is only one "side" of a ring-shaped map. Now THAT would be huge. Probably doesn't make sense though.
I do think the map looks weirdly elongated though, like it's a "corridor", which is pretty uncommon for an open world game. Good way to gate progression though, Tsushima did it pretty much exactly that way.