I sorta started incidentally watching Lovejoy in the 10-11 season, during which I was unemployed during the entirety of the season and watched an insane amount of hockey on Gamecenter. I was watching Pittsburgh a lot as I had started following Letang a bit by that point.
Lovejoy is a very good skater for his size and plays a very sound positional game. He also plays the body a respectable amount as well. I wouldn't call him a hard hitter, but he does a great job of using his frame to pressure opposing players (and his good mobility in pretty much every mode of skating to get him into position to do so).
On top of that, Lovejoy is a good puckhandler. He's not going to wow you with his moves, but he is solid at retaining possession. He also has a very solid and safe pass, and a great first pass. He's not the guy looking for the awesome offensive setup, being very much a D first guy, but when he pinches or moves the puck in the offensive zone he does so responsibly.
The advanced stats over the past 3-4 seasons back it up as well. Lovejoy is extremely effective when on the ice, and his team tends to do more poorly when he is not, particularly defensively. He seems to have very good PKing numbers as well--while he does not get high ice time, he plays against a very high QoC and does extremely well.
I'm not willing to chalk this all up to randomness, as these numbers persist and have backup over several seasons. Rather than the sporadic up and down you tend to see from players perhaps benefiting from fortune, his numbers tend to show steady and consistent improvement with steady increases in ice time, what you would expect to see out of a developing defenseman, particularly a 2way/defensive dman. Curiously, one thing that the stats suggest is that Lovejoy may need to see more PP time. While he is not a direct producer, it is possible that his good pass helps his team effectively enter the zone, and he is good at containing the puck within the zone.
As for the eye test, well, players like Lovejoy are hard to eye test short term. He doesn't create offensive highlights, and he doesn't deliver constant bonecrushing hits or anything of the sort. A lot of his best work is simply being in the right place, using his good skating to get there, stick on the ice, doing the dirty work in the corners, etc. There's absolutely nothing that stands out -- and sometimes, that's the best thing for a d-man.
My conclusion? I'd like to see another full season out of him, but perhaps the OP has a point. It's possible Lovejoy is developing or has developed into a very good defensive d-man, and he may even have a bit of PP upside (though not necessarily in the points department).