He's taken on a militant but disorganised union with no clear motives for a strike which was voted for by gullible and ill-informed members who phoned in sick in their hundreds. He knew BASSA couldn't deliver a result for their members which is why he called their bluff.
In contrast, BALPA led a focussed and well researched single issue campaign. WW knew they could deliver an effective strike, not a sick-out and not a "vote yes but I mean no" campaign. That is why the pension lump sum went from £500M to £800M and the annual payments went from £250M to £280M. WW could wipe away Bidline and still wouldn't save that sort of cash. He was willing to cough up that sort of cash to pay off the pension deficit because he knows the pilots are the only group that have the balls, commitment and financial resources to deliver a prolonged and crippling strike to BA. Thats why the man who only consults negotiates with us.