With the new changes I was thinking that adding a 50% slow effect to expertise mode would be good, so you can't walk around for free +5 armor class. It would show you being in a defensive mode and limit what you can do and really put you in some danger being slowed down.
Maybe an update to the 'examine' tool as well. Since we can see if people are in stealth/detect, seeing if they're using another combat mode would also be helpful. Since otherwise the only way to tell if someone is in expertise is if they're actively swinging at you and you read the combat log?
Isn't the minus -5 to attack, and it being deactivated upon using any other useable good enough for nerf?