Okay so hum. Playing this was one of the most frustrating moment I have ever experienced in TF2 !! There, that's said, now onto the constructive criticism
BLU spawn : I'd suggest walling off the setup gates with respawnroomvisualizers. It's not mandatory (dustbowl doesn't do it), but it's kinda expected that RED players shouldn't be able to get past that point. BLU's spawn times are also messed up (I think), need to be shorter.
Overall : Too large (a bit), too open (a lot). You could put little houses and even bigger building in the middle of some areas and it wouldn't fill up all that empty space. I suggest you do just that, in fact. Or some rock formations if you're going for the absolutelety desertic desert look, or anything that can take up some space and break up those sightlines and gives us a chance to maneuver around unnoticed.
Cap A : capture area is too small. Capture time might be a little unnecessarily long. Otherwise ok.
Right after cap A : there's a major chokepoint there that is veeery bad. At least potentially. This requires another route, or something. Also if you can get rid of the opening and closing doors that'd be nice (protip : as a demoman, right click when the door opens...). Come to think of it, that area is probably very badly optimized, I think it's possible to "see" from behind that chokepoint into the BLU spawn. Put some walls, turn it into s or c shaped corridors or something.
Cap B : Very hard to capture. Put fences or something to block players from being blown into the pit too easily. Cap area is small too and capture times feel long for a final cap that is so much in favor of the defenders. Otherwise, sure why not.