There is no current reason to add this feature into the game. I'm fine with it actually displaying the level difference between myself and the monster for anyone who cares about this for some reason. However I see no point in penalizing experience points in the current state of the game. You can't just partially "balance" experience point gain. Unless they are planning to nerf all exploits of experience points such as Abyssea and Grounds of Valor, there is absolutely no reason to add this.
The development team and some players in this thread might see it as proper balance but it really is not. So I'm allowed to exploit experience points by taking advantage of being power leveled through Grounds of Valor pages? I'm also allowed to key chests or stand around in Abyssea, while someone with item level 120 weapons destroys mobs? But it's imbalanced to actually work on experience points for any reason with my own hard earned gear?
Like most players are stating in this thread, focus on something that matters. This balances nothing, it is just a nerf (not a big nerf but a nerf nonetheless) for no real justifiable reason in the game's current dynamic. If I put in the effort for getting the Delve boss win and 200,000 plasm, I deserve to go into older content unhindered and grind it to dust, laughing along the way. There is a sense of reward and progression that is noticeable, which is fun.
I get the concept that you're stronger but unless you're going to treat the entire game with that methodology, I see no point in doing so to only part of the game. It's more ridiculous to me they are spending development time trying to balance this versus fixing real problems with the game.
Don't spend time replacing perfectly working pipes when you have septic tanks leaking elsewhere left unrepaired.