Tough to call NXT developmental with guys like Bobby Roode, Joe, James Storm, Drew Macintyre, Eric Young, etc... all recently going through the promotion. Lots of gray areas there.
Just because older or more experienced wrestlers go through the promotion doesn't mean it's not developmental.
With those guys, it could be developing a new character, it could be developing mic skills, it could be as simple as a better way to reintroduce them to the WWE audience, it could be developing them to the WWE style.
NXT is 100% a developmental brand, even if not everyone that goes through there needed major development.