Conversely, that was also one of the dumbest powerups.
But, He's awesome so it doesn't matter.
Spoilers, I guess.
Also, the captains coming to save the main characters was stupid. They beat them all, so why can they beat someone they couldn't? Especially when they didn't have any discernible power-up.
That's not strictly true. There are a lot of things you have to bear in mind before making statements like that.
And just because you didn't see it, doesn't mean the captains hadn't gotten stronger between now and the Soul Society arc.