I wouldn’t think that to be “normal”. My XLT is several years old and I don’t have any yellowing/browning, from heat like you’re showing. I’m sure a quick call to Wolf/XLT will answer your question.
I got rid of my XLT partly because there was so much heat coming out of the ends of my oven. We package our tenders in foil and generally open them up on the entrance of the conveyor platform. With the XLT if you were not at the very end of the platform, your hand would feel burnt within seconds. My store was hotter and my A/C had to work harder. It’s a shame cause it cooked a great pizza.