Logic would also dictate that a company would use the pilots from the aircraft that the new types have replaced.
Logic also suggests that if the new type carries more passengers or is faster - allowing more sectors per day - then there is a potential to reduce the number of airframes required in the fleet. That reduces the number of pilots required.
Logic also dictates that if the new type replaces several different types then the number of reserve crews is reduced. That also reduces the total number of pilots the company needs.
Logic continues to dictate that the trend towards utilising maximum permitted flight & duty hours for crew reduces the total number of pilots needed.
Only if there is an increase in the number of airframes required OR possibly in increase in the utilisation of the airframes OR a more limiting regulatory change in FTLs is there an increase in the number of pilots needed.