Originally posted by: AssertnFailure
byakuya's shikai is pretty much like that one guy ishida fought who turned his sword into lots of small flying blades, except better...

the problem with shikais like that, is that the actual skill/strength/speed of the attack is beyond your control. Unless there's a way to train his sword to cover more range or flow faster or something, it's pretty much capped. Then you have shikais like renji, where it's an alteration of the sword that is still completely in the user's control. In those cases, the user can still develop their skill, strength, and speed of the attacks as necessary.

In other words, even if ichigo beat renji's shikai, renji can still develop his shikai further to prove a tougher match next time, while once byakuya's is beaten, then he's pretty much screwed (at least as far as shikais are concerned)
Well, in the world of Bleach physical skill, strength, and speed means shit... It all comes down on your spirit level and how you gain control over it... so as long as you can improve yourself in the spirit department, every shikai should improve...