About the aura around the swords, I think it was done on purpose to show the difference between the first use and the proper KoH attacks, basically rewriting what Oda did.
1st attack is with that mid aura covering the swords, crude use of conqueror's haki.
2nd attack is the first KoH attack, mid use of conqueror's haki.
3rd attack is the finishing KoH move, perfect use of conqueror's haki.
Bird dance was just to show that Zoro can use conqueror's haki coating at will with any sword and that he doesn't need to go all out with his haki.
Agenda Piece loves to pretend that Zoro can't use CoC without a sword or that he has a time limit and needs to go all out to use it.
