I agree with weit that railings should have no collision due to valves decisions on their own and updated maps, but this could actually solved by just changing the railings from being... railings. Outside of IT is a fucking meat grinder with the railings for anyone, removing the collision only makes the problem worse.
If mid railings were to be changed the concrete pads to either side of IT should to be lowered (and thusly like 1/3rd of the mid to ensure the highest points of the floor are at choke) in an attempt to give some cover for whoever , similar to snakewater's use of terrain to provide something similar to what the railings currently do. (This being high ground/sticks are almost always guaranteed to get good damage on while spam or bad aim is punished via using the small amount of verticality the floor gives you.
the platform above mid sewer entrance and making openings at least 144 would be a small but impactful QOL change. Arguably it would make it easier to skip/speedshot some more entertaining routes but either a) theres a fucking shutter there or b) theyre enclosed enough and far away enough to make any viable bomb require a reload or another body in the fight.