Here's a recap, a much weaker Ichigo drawed with kenpachi with a mere shikai...
Ichigo with a basic bankai and black getsuga defeated Byakuya's ultimate move...
Now Ichigo gets his assed wiped by Grimgow a no.6 arrancar using Bankai and hollow mask?! That fight lasted ages before Ichigo found "resolve" to beat Grimgow. So if a number 6 can fight on a much more powered Ichigo, numbers 5 and bellow should be wiping the floor with the captains. Unless there are huge gaps of power between the captains, they are pretty much boned.
Also how come Ichigo can barely take on Grimgow (6), but Kenpachi can take on number 5?! Shouldnt their levels be about the same? Was Kenpachi really going easy on Ichigo back then?! There is much inconsistency with power ratings in Bleach, that its confusing... Either Kenpachi's "kendo" is THAT much stronger, or he was toying with Ichigo back then, or both.
As many have claimed, Vaizards should be above the captains since they WERE captains before, and found a NEW strength which they managed to overpower... Although I doubt that a single vaizard can take on Yamato- who has been a Captain long before anyone...
And I don't think the Vaizards will fight the Captains, it was Aizen who caused them to be kicked out of soul society, etc... So it's pretty clear that their main target would be Aizen.

