Is this more burn in than normal?

It's normal... on an LG display.

It's not normal on a Samsung display.

And that's not to say all LG screens have that, but... I don't think anybody can prove that there exists an LG retina screen that doesn't have any image retention.

With that said, I think you should check it in with Apple if the "burn in"/"image retention" bothers you. They'll most likely swap it for a Samsung display, which has yet to be reported as showing any image retention.

 

If you can convince them to replace the screen, they will say they cannot pick what manufacturer your next screen will be, since that's their standard operating procedure. However, you can quickly tell yourself whether or not you are getting a Samsung. Before you sign the work order, make sure they select the clamshell part that has something like 661-7171 as the part number. I don't remember the exact number off the top of my head, but it's the one that is something like that, not the one with 58 in the part number (620-5813?). That's the LG. You could probably google it to find the exact part numbers for the Samsungs and the LGs.