Also I'd hardly classify funeral plains as "open map" since it has tons of hills/ridges on the sides blocking the efficiency of massed spam/pushes while the middle is hard to push through due to the fact ACUs tend to hover around there + it's the easiest spot to pincer enemy attacks at and convert them into a mass donation. It's like calling Canis an open 2v2 map just because it has some flat terrain in middle.
Open map to me is more like playing Wonder Open in a 2v2 where massive tank spam must be done or you will get raided to shit. It's the inverse of closed map, rather than make no tanks I make nothing but tanks.