As a year round commuter in an area with four season my thought on commuter bikes is this: I'd want to have the lightest, fastest, and most modern bike I can afford to have it ravaged by wintry elements, or in the case where the bike needs to be locked up, to have it stolen.
As far as comfort is concerned, after riding so many years on exclusively drop bar bikes, I would never ride a flat bar bike for any length of time if I can avoid doing so. You just have to go with whatever you find comfortable with your road and gravel bikes, and stick with that.