Kriss, please I beg you stop talking about things when you have clue about them. "Out of the blue presumptions" do not help to generate a positive drive on the topic.
The size of the campaign map size is a quite unrelated issue for the memory limit, why the heck you get me raged so easily

The lack of seasons on the campaign map in the OP is just an example for many other things, which are degraded or limited in Rome 2 (battle animations, unit variety and texture variety, night battles, cities (are very cool now, but could be even better for sure, the textures and buildings are very repetitive (more variety cost more memory) and so on.
The vote you voted possibly with no already, is essential for the FUTURE of this game, even you do not have right now a proper hardware to participate. But with your next upgrade you will understand my valid concerns, which are backed up now twice by CA staff.
It does not matter how big the campaign map is in "Medieval 3", and it would be very sad if memory limits would lead to a smaller one as you expect it to be for geographical reasons or whatever.