It's OK to think it. It's OK to say it. It's even OK to sing it, though I'm not sure why you would (unless you're one of those people who walks around singing stuff. Which, to be fair, I totally do. Drives my wife insane).
Fisher, as recently as earlier this season, was a bust. He'd lost his LT position due to poor play and was on the verge of being benched. None of what I just wrote is true, but it was the narrative nationally and even among many Chiefs fans. If you were to browse through the comments here, or take a quick trip through Chiefs Twitter (a dangerous place for any player, to be sure), you'd come away with the conclusion that Fisher is an awful player.