The nerfs aren't really necessary, this isn't a PVP game, it's a PVE game. Even if you decide to nerf, by being transparent you'll maintain trust with your players. By making all these hidden changes that aren't disclosed, you erode trust from your players and kill the joy of playing the game.
Upgrade materials don't respond, the mats for making upgrade materials have such a low drop rate that farming them is a huge time investment, then you nerf items in the game that players have invested time and materials into really just screws your players.
You will start losing players if there aren't any serious changes, the game still has numerous bugs yet you guys for some reason decided to focus on nerfs instead of fixing the game.