Butler is a lockdown corner, special things happening with the Colts.
It is great he found his niche with the Colts, but for him to be considered a lockdown CB he first needs to establish himself as a starting CB. This season and last he has been the 3rd DB in for Nickel and Dime packages.
NE was a terrible fit for him because it was a high pressure environment where DB's at the time were the biggest weakness and they were very quick to change the lineup if someone was struggling. He struggled quote a bit in that system and I am sure lost all confidence. When he joined the Colts they were a team with zero expectations who just unloaded every impact player on the roster other than Reggie Wayne. He was given a longer leash as a Nickel DB where he was able to built confidence with other off the radar/younger players.