I think he still has quite more in him. If it wasn't for the injury, this would be true already (same can be said of.others, course).
Apart from the results, what made me sure he was out of the curve was a series of finals and important matches he had with Nadal on clay. He lost some, won some, but them all were with an absurdly high level of quality *and* intensity, non stop. Most of the names quoted above could not even dream of doing that.
As for Lajovic, he never made headlines. Overall he is a decent top 50, his right on average physical skills will never let him go much better than top 20 (where he stood for a while).
But his shots, from both wings, are just marvelous to watch. And a very beautiful, even if excessive at times, point construction. Also, I really like his attitude. He competes, but with dignity. No shouts, almost invisible fist pumps, respect and gracefulnes to adversaries. In other words, I want to be just like him when I grow up...