1) There are animated arrows on the lock screen showing the direction you need to drag it.

I was thinking more of unlocking using the keyboard only, but I'm sure many would agree that the swipe-to-unlock gesture that that is(,) is not particularly well-suited to users using mice.

2) Pressing Escape to dismiss things has been a common pattern for years.

True, but I don't think that this allows us to get rid of elements that can make the user more confident in what they think the computer will do. (pressing the OK button to dismiss a dialog vs. hitting ESC and hoping for the best)

3) Windows 8, 8.1 and 10 have a similar lock screen shield that is dismissed in the same way.

So is this shield behaviour justified because of potential emigrants from Windows to GNOME or because Windows has Microsoft's backing?

this is not the right place to discuss upstream design decisions.

You're right, I'll stop

-Marco