Guardians were always the weaker class in comparison to shadow and powertech before, it has only been after 2.0 that they were rebalanced. So no, Guardians are not op in the slightest, they were weaker before and they are at the place they were supposed to be in the first place.
Threat wise, yes. Juggs have been brought into line and now all three tanks are quite comparable in terms of tps. The tank balance itself though, got thrown out the window when they changed Jugg mitigation (which was always well balanced pre 2.0 with the other tanks).
Jugg tanking is all pros and no cons I'm afraid, we have the same damage profile as a vanguard tank with the best cooldowns in the game, and also our own version of force shroud: saber reflect. We were literally given all the things that made the other two tanks stand on their own. Juggs are hands down the best PvE tanks in the game right now.