The thing is, though, that as long as it was legitimate to get long term injury relief for him at some stage, they're within the rules.
I went carefully through the collective bargaining agreement looking for a requirement that a player come off injured reserve (and the team stop collecting long term injury relief) when the player is healthy enough to play. When he's first hurt the team may (but isn't required to) put him on injured reserve to use his roster spot, it may (but isn't required to) collect long term injury relief against the cap hit any time going back to his original injury and they may (but aren't by the rules required to) activate a player when the player is healthy enough to play. I was really surprised, but could find nothing that said a player must be activated when healthy.
Possibly something got missed in the CBA or, more likely, a decision was made to allow some flexibility so that players can work themselves back into shape in practice rather than go straight into games as soon as the injury has healed sufficiently.
So far as I could find it is perfectly legal to hold a player out for a while after he is healthy enough to play.
However frustrating it is to see teams gain an advantage that way, there's no point in complaining about breach of rules when the rules aren't being breached