The gear score of purchased items should not be nerfed not because it is unfounded but because this will create a greater divide between players and their commitments to grind.
Understand that you want to reward the players that commit to the grind and are always pushing towards the end game gear nerfing purchased gear will be one of the biggest casual player killers.
A compromise to this dilemma could be that gear between 500-600 should not be affected by a players expertise as this will actively discourage casual players and crafters from participating in mutations and PvP content as their gear will not be on par with their peers leading them to feel underwhelmed by their predicament.
The increase to gear score and from 600-625 is good as this will showcase the people that participate in the end game content and have a large commitment to the game while not being complete gated by the 500-600 grind.
The belief in this mainly arises because stalling players progression aka time gating is a very easy way to sway a lot of new and casual players from participating actively in the game many of my friends have already quit due to the long grind, and time gating the 500-600 grind will unequivocally see a drop in crafters and casual players.
It is my understanding that to get gear to 625 you will need to commit time and resources to individual items to progress them to the new max gear score, gear that is already bound to the player gear that can not be traded, gear that will need to be swapped around so that players can adapt to the new expedition’s which will require them to grind the expeditions again, gear that needs to be 600 to be upgraded.
In this instance, It makes no sense that there should be any time gating for players to obtain 600 gear score items if this is to be the new system as the player will have to consistently increase the GS of new and better loot to adapt to any new enemies or system the game may throw at them.
In summary, the gear between the levels of 500-600 should not be nerfed for any player as this will create too much of a time gate for crafters and casual and the introduction of the new mutated expeditions and the new 625 GS grind will create a significant enough challenge and goal for committed players.
PS: Please bring transmog into the game especially with the inclusion of this new system and how it functions and the ability to colour skins this will open up a variety for customization and allow for people to integrate their skins with current armour more seamlessly which will encourage the purchase of more skins.
PPS: If this nerf goes through as a casual player I may have to reconsider my commitment to this game.