Federer is a bad matchup for Djokovic, specially outside of HC.
I disagree. Federer is not a bad matchup for Djokovic. Djokovic doesnt exactly struggle against Federer, he has the game to beat Federer maybe even when Federer is playing close to his best. The thing is, this works vice versa too in this particular match-up. Thats not the case for Nadal-Federer or Nadal-Djokovic.
Most of the time, Federer's matches are in his own hands, it has a lot to do with how HE plays because Federer is usually the more attacking player and when he gets it right, it becomes very hard for the opponent, whoever it is. Its the same with Novak that is all.
And as you say, outside of Hard Court, Federer's best on the other surfaces still trumps Novak's best. Its very very close on clay, but on grass, Fed's best would have dismissed Novak (but sadly Federer has declined horribly on grass offlate)
But overall, Fed is not really a "bad matchup" per se for Novak.
Federer-Nadal. Federer-Soderling...Now THOSE are the real bad matchups.