Sorry I tried to be clear, I’ve only played the TW3 main (Realms of Chaos) campaign. I don’t know if the new campaign/map will run the same or worse (possibly better, but I don’t think so). Its definitely a case of even with the TW3 campaign map running worse I think the map looks better than TW2: Mortal Empires (there’s not any overlap with the Vortex campaign I believe, so harder to compare).
So, its your second point (“even running worse you can put up with it due to the new map being much better”) but I stress I am only talking about the TW3 Realms of Chaos map as I won’t have access to the Immortal Empires until you all do (unless you got some early access).
Edit: Okay so the best comparison is from that video @Scotch_Lufkin posted.
Here is the Silver Road in TW2: Mortal Empires (sorry there are no armies or much visibility)
Here is the Silver Road in TW3: Immortal Empires (snipped image from the above YouTube video)
Here is another, this time Reikland from TW2: Mortal Empires
Again, from the YouTube video, Reikland in TW3: Immortal Empires
Hope this helps!