Why move the delete button?
For 20 years, to delete from both the inbox and message itself, you went back to the top left (beside the select all). Now some wet-behind-the-ears jr developer thinks it's more important to hit reply than keep things the way they were once you are in the message itself so your 20 year autopilot has to be relearned and you have to remember where you are to speed thru the hundreds of emails one can get in a day. Perhaps the developer replies to every one of their emails and doesn't mind wasting time bouncing around the header but I probably delete 50 before I ever reach one to reply to. So the auto pilot of going back up and left is now up and left for the inbox but up and right for the message itself. What a moronic change and probably only useful for 1% of users.