If you guys are actually concerned about the rate of XP gain, you should probably go back and take a good, hard look at Abyssea and Grounds of Valor.
All this is going to do is make it difficult to complete XP-based Magian Trials, with Augmented Relic pieces suffering the most since Dynamis monsters are already on the lower end of the XP-curve at 99.
There's also the fact that most players learn about gear-swapping eventually, and most players tackling difficult content are expected to do so to perform well. Our effective level will be changing frequently as a result. There's not going to be any real benefit to this system when most of us only wear a few pieces of the newer gear. Older gear is still often optimal for different purposes, and the current design structure of "one size fits all" for new Adoulin gear suggests that this will continue. No Monk (for example) is ever going to wear Manibozho Gloves.
The development team needs to take a step back and think about how we actually play the game and reconcile that with how they seem to *want* us to play the game. There are some stark differences between these two things.