Not directed at you Thee but lots of people have said he has declined, like it had something to do with his skills declining. Lauri was also declining when we got him.
Collins was working that whole time with possibly the worst offensive mind at HC in Nate McMillan. Everyone knew he was misutilized big time, but since Nate wanted to run guard heavy offense JC was relegated to cold hands catch and shoot only.
Bear in mind he shot 80.3% FT last year with that finger (2nd best mark of career) and right after Snyder came in to replace McMillan he also raised his 3P% back to the 37-40% range.