I feel that a player's overall contribution to the team is more important than his contribution in one aspect alone.
A player's overall impact on the team is more important to consider and if the player is an alltime great in one aspect, that has to be kept in mind as well.
Imran was an alltime great bowler, slightly behind Hadlee in my opinion. Both are competent and capable of leading an attack, even one as special as this one. The difference between bowlers like Imran, Hadlee, Marshall, Ambrose, McGrath, Donald, Holding, Wasim, Trueman, Garner, etc. are very little in their area of expertise ( pace bowling).
However, Imran is significantly better than Hadlee when it comes to batting and he is a very good candidate for being captain, as this alltime great team lacks a genuine alltime great captain ( bradman was good but not in the same echelon as some of the greatest captains while the rest are at best 'competent' in this regard).
Owing to this, Imran would be more valuable to the team than Hadlee IMO.
Its a bit like debating whether one of Tendulkar/Lara/Sobers/Richards etc. is the best batsman after Bradman, but Sobers being easily more valuable than the other three as a cricketer ( The gap between Imran and Hadlee is not as much IMO but Imran is more valued a cricketer than Hadlee IMO).
Infact, the only other challenger for this position is Keith Miller IMO as he was essentially a lot like Imran Khan in terms of impact to the game - great bowler, competent batsman and an excellent fielder.
My last four would be Imran, Hadlee, Marshall and Muralitharan.