Travel distance to the final area is rediculous, and there's no real position to build a sentry nest where BLU engi's can protect their teleporter exits.
This whole area is nothing but a buffer. I've never witnessed any real battles here, ever; and only serves to allow BLU to milk some cap points off the cart and RED to set up defences that never get used because battles amount to a bunch of skirmishes at stairwells around the circular pit. A buffer wouldn't be a problem if the route wasn't linear and stretched the final objective as far away from the BLU spawn as it does. Get rid of this area entirely and maybe loop the track back and forth so RED arn't steam rolled.
RED's only real chance of winning is at the location with the bunch of scribbles. The height advantage, rollback and choke make it almost impossible for BLU to push forwards and gain some territory and the choke also means a single defencive pyro can ruin a coordinated uber push with a couple airblasts.
I remember playing an earlier version of this where sentries nested in the corner to the left of the ramp. The problem was with all the rocket and grenade spam from the ledge directly forwards and to the right, noone could reach the top of the ramp with enough health to challenge a nest of level 3 sentries. The second issue was that the medic had to make himself vulnerable for too long before assaulting the positions beyond the ramp and was prone to dying from spam explosives, spies or snipers.
Through nothing but sheer luck in the closing moments of the round my sticky bombs took out the engi despite being airblasted away and some of my grenades finished the gear off. Only then to have the 2 remaining engi's replace all the gear and lay more before i even got back and the team to push forwards.
With this in mind you should probably place a room here (as indicated by the scribbles) to cut some of the horrendous sight lines and reduce the area of control for RED by creating a safer flank.