I agree with Rex. The number of pilots required in BA is driven by lots of different things (retirements, part time working, avaliable slots, business plans, numbers of aircraft in different fleets and crewing ratios, training capacity, simulator availability, projected sickness levels, rostering systems, etc).
The Pilot Recruitment Manager and his team run the numbers and parameters and eventually come up with the plan (which varies frequently) in conjunction with BALPA. This plan includes recruitment.
In practice, replace person A with person B and you end up with the plan. The personality won't change the plan as much as you imply, the other factors will have a greater impact.