Well, just couple of thoughts

[GrafBlade]

well nowadays we have the problem of more grinders than halberdiers so there has to be some usability fixes on that. as Halberdier has around the same armor as Crossbow heroes i assumed that it would fit best that role, Armor Wise its Archer/SKirm/Xbow/Inf. with halberdier lying between Skirm and Xbow armor Wise.
Also as there are Fewer Xbow Bots than other Type of Bots, the chance of Heavy Sallets to drop is fewer than for example Barbuttes (Nord Vet Pikeman) or Ornates on Einherjar Pike (thats hard and rag bots) whereas Xbow can only loot Helmets from Rag bots (Dvergar/SM?)

Or Maybe Zweihander/Legi?

Well, you're right, there is a decent amount of Grinders around, tho you haven't seen them that much anymore even before 1.5. I generally agree that Grinders could use a 2nd hero class to be used
on, but definitely not on xbow imo. (This would just cause a vast amount of stat changes and I think that xbow's are fine where they stand now-->armor wise)

Concerning the drops: The past has actually shown that's it the other way round. I at least got the feeling that Barbuttes were hardly purchasable, also caused by almost no Barbutte drops in the last year or so.