Wearing Gorget/Belt/TP Bonus Moonshade boosts it back up to about 4 fTP, but I agree that it probably should have been 5-hits if they were going to put this mechanic on it.

Drakes is 4-hits, Crit, and 50% STR. Polearm base damage is substantial.
Stardiver with 140 STR:
127 (WSC) + 146 (Rhongo 95) + 10 (fSTR) = 283 base damage
322*3.93 = 1112 Base Damage*fTP

Drakes with 200 STR:
63 (WSC) + 146 (Rhongo 95) + 10 (fSTR) = 219 base damage
241*4 = 876 Base Damage*fTP

So (in an extreme case), Stardiver has a ~25% base damage lead over Drakes. Drakes has a 20-30% crit rate in WS gear. Crits increase pDIF by between 50 and 100%. As it is, it's hard to argue that Stardiver is an improvement over Drakes except in very strange situations where you're fighting EP monsters with buffs and a low crit rate/Damage. If cRatio drops (high level or high defense targets), then the value of crits goes way up and bridges the gap. If Crit rate or Crit Damage goes up (like in Abyssea), then the value of crits/being able to crit goes way up and bridges the gap.

Overall, it lacks a fifth hit. It also lacks a useful WS property. It should have been Fragmentation.

Edit: I guess it is worth noting that the Weapon Skills category is headed with "Group 1." Assuming that "Group 2" enhances "Group 1," we perhaps shouldn't be so quick to judge.