Don't. I've been playing this map forever on the server (24-man, vanilla spawn times) I play on, and am a bit confused by all the nerfs to RED you're having. It's pretty easy to win as BLU already, and more often than not both teams win on BLU and lose on RED. That window sentry is very easy to take down from the far right by soldiers or demomen or snipers or anything really.
Perhaps, but not many players actually take the path to the right. They see the CP, and the catwalk, and want to push head on through. Although this almost always fails, I don't believe in forcing players to act against their instincts, or blame them for not taking the alternate route. Instead, I want to be giving players a choice, rather than punishing them for not playing how I'd like them to play. Ideally, The catwalk should be as viable as the other route. That way, nobody is frustrated, and nobody would feel the need to blame me for making one of the potentially easiest cap on the map, impossible to win.
Of course, I have yet to personally test the double-catwalk layout, but if it's needed, I'll make the side path harder. I've seen far too many matches stall there, and everyone feels frustrated. I believe the first CP in these stages should primarily be a "time-waster", and not be an actual "winnable" point to defend. Asking around, players pointed 3-1 as their most disliked CP, which I'm not really fond of either. Balance should always be a focus when mapping AD maps, but my goal is to make it both balanced AND fun.