Why it moved is covered here:
The main reason is that we had reports that it was unclear your username was a clickable button, which lead to people having a hard time finding log out and their preferences specifically. I haven’t heard of many issues with discovering the clickable tabs in the menu, so going that way seemed best.
I agree that the gear icon isn’t the best representation of everything under the menu (would a user icon be clearer? I’m a little skeptical). The gear icon is very clear for preferences of course, and it’s not unusual for other sites to put the log out link under a gear icon either (Facebook is one common example).