I didn't say it was impossible to escape on the surface, but for me (a DiD player) it's not worth the risk of being caught out by a searchlight. Early war, ASDIC is so bad that escape is a doddle under the waves in GWX. Surface escapes are possible - maybe even
probable if you know what you're doing - but if you do get unlucky and you're caught on the surface by a spotlight then you're in very big trouble. That's why I recommended the submerged escape route.
Why don't you try a surface escape and see whether the game models it in a way you like? I doubt any amount of discussion will really answer your question as well as a test.