This isnt historically accurate, even in the ancient times only small ships could pass through, for most of eu5's timespan it was fully closed in fact (see: https://claude.ai/share/55ba418a-b11d-4642-aa0f-dd2883802c34)
hell its still barely passable today
More to the point its existence is detrimental to the gameplay, as one cant control the entrance to the baltic sea and the populated norwegian south by jut controlling the two sea zones betweet Jutland and Norway