Maybe there's a bug, but weapons are becoming more important for threat as the current ilevels mature. A Zenith relic isn't good enough to hold threat against high powered dps. And while average ilvl is important for tank survivability, it's a bit misleading. The weapon ilvl is the main factor for building threat.

I still have no idea why FFXIV doesn't simply bump up tank threat generation. In almost no other MMO do tanks have to fight so hard for aggro. Usually tanks are responsible for using their abilities, interrupting, positioning, targeting the right enemies. As long as tanks are attacking, basic aggro isn't a problem. Tanks usually need to worry about gearing up their armor more than making sure their weapons are top notch ... and then FFXIV tanks still have terrible dps (compared to real dps classes) even with decent weapons ...