What could be more important than the weather (Excluding the boat, naturally)? The weather influences every decision you make Do you attack? Can you? How close can you approach? Can you do it from the surface? Can you be certain of your target's nationality? How about range?
The accuracy of all of this information you need is directly influenced by the weather conditions, and then the final decision you make based on these observations is also dependent on the weather. Weather is as important to a subsim as it is to a flight sim. It should absolutely be a top priority from day one. I hope they get it right this time, because in SH3 it's a joke. I don't play much SH4 so I can't say anyting about that.