It depends on what you judge a masterpiece by. Is it an album with every song being good or great? An album with many great songs, some good songs, and a couple duds? Some other standard?
I judge the masterpieces by that first criteria. "Achtung Baby" meets it as I can't think of a single below-good song on it. Good tracks = "Tryin'" and "Zoo Station". Great tracks = everything else. If there was only one album I could listen to on a desert island, that would be the one.
As far as TJT is concerned, it is the album that made me a U2 fan. AB is the album that made U2 one of my favorite bands, though. TJT has three of the greatest songs that U2 ever produced, a few that are in the higher echelon of U2 tracks, a couple that are good, and a couple that are sort of meh. Obviously, it has the strongest 4 consecutive tracks of any U2 album, but I don't think that is enough to make it a masterpiece.
When I first heard about U2 playing the album in its entirety for an entire tour, I was not in love with the idea. The reason why is because of 3 of the last 4 tracks of the album. They're not exactly interesting tracks. I mean, each are decent in their own way, but they're not tracks that enthuse the crowd the way the first 7 tracks and OTH likely will. You could play an album like AB in its entirety, do a Zoo TV-type concert throwback and you'd have crowds singing along/excited about every single one of those songs. I can't see people reacting in a similar way to "Exit" or "Mothers".
So to sum it up, no, I don't view TJT as a masterpiece. I love the album and it is one of my favorites, but very, very few albums are masterpieces to me.