Personally, I don't think the CT health boost is op. I think that the Ts are actually op, they can have a gun and stack in each other and the CTs cant to anything except to tell them to unstack. Anyone who plays both sides should be able to see where I am coming from. Often times, the Ts win the round, especially when there is 1 CT left, this is why health boost was implemented in the first place, sure its annoying when you do 150 damage to a CT who used ctbuy menu mid fight, but understand that the menu is to try and help the CTs enforce.
If anything, I think the last CT should automatically get 135 hp once their teammate dies to give the CT a chance to regain control of the prison, but this will interfere with the current LR plugin by giving the CT 135 hp when in an LR and their teammate dies. Or we can give a CT health when they get a kill, but this will be abused and lead to many many problems.
I know this thread is about the CTs being op, but I think that the Ts are the ones that are op. Generally, things are balanced in my experience.
Edit: Buffing the health-shot to give the CT 135 hp and removing health-boost doesn't sound like a bad idea to me.