There is a stat-cap in every dungeon or raid.

Usually any gear that is above the dungeon/raid level will get scaled down to this cap.

I've got a perfect example of this. I was in one of the Crystal Tower raids. They are level 50s.
I was playing a Gunbreaker. Figure I was 70 or higher at the time.
So I was at the stat-cap for GNB while inside the raid.

I was jumped on by one of the other tanks for stealing aggro. His argument was that he was wearing "level appropriate" gear for the raid. Meaning something around 50.

I was barely doing any rotation, hardly paying attention. Never using Provoke or my ranged. And still stealing aggro pretty strongly.