the DL PC on BCCH timeslots is never active, but UL PC is active (if enabled).
Power Control is not active during the SDCCH estab phase, and usually not active during the SDCCH phase neither.
So disabling the UL PC cannot improve the SDCCH establishment (it just can’t), and it may slightly affect the SD Drop (but i doubt it). What you are seeing is very strange…
If you see an improvement, then it has to come from something else. Please share the SD Estab% and SD Drop% values here, try to roll back, and let us see the changes. I need to see it with my very own eyes 😀