He said in the beginning of the season that he's been cut off from Heaven so there are certain things he doesn't have full capability of doing such as healing and time travel. This doesn't necessarily mean his powers are slowly draining away from him episode by episode. If that were true, he would have been completely weakened by now. Instead, in the last episode Castiel seemed to possess a bit more power than we've seen from him in previous episodes, and perhaps even more badass than when he did have full capability of his powers from last season. So in my view from this, Castiel is only limited to certain abilities rather than losing them, as he's already stated in 5.02, since I'm sure to him this does feel like he's been weakened or made helpless because of being cut off from his home, but certainly not weak as in feeling his Grace drained from him. As for the 2014 future!Castiel, it's my belief that when the angels had left and Lucifer took power that is when he became completely powerless and "no longer an angel" (at least somewhat, he's still an angel just trapped inside a human vessel). Not before, not along the way, but in the moment when Lucifer had taken control did that occur. And even though we're now seeing Castiel subtly become humanized by his mannerisms with each passing episode, he still has BAMF skills and his some of his powers intact.
Overall, from what I've observed, I think with the knowledge of him having limited access to certain abilities people are confusing that with him losing more of his powers, especially since we've seen over the course of this season just to what extent does this limit him to.
Now I don't know if there's been any kind of articles or interviews explaining whether he is or isn't gradually losing his angel powers, since I don't read anything that could have potential spoilers in them so I don't know if this has already been discussed or confirmed or whatever. These are just my thoughts and opinions on the matter.
This is just me, having thinky-thoughts at like, early in the morning. And it has to do with Castiel, go figure. Heh.