you weren't kidding about it being damn large
don't use cube barriers and it would be better. replace them with a simple slope down to the ground and let people walk out of the map if they want to; its not like there's anything there for them to do.
as for the center of the map (which i assume is the stuff shown in the second pic) it looks pretty sparse and nonforgiving, since there's pretty much 0 cover and no terrain
try making shaped flat terrain so its not so basic and impossible to find cover. if you don't know what I mean check up the
terrain guide, under brickscape flat terrain