The problem is that the ovens were made smaller some years back. I think they also thinned out the metal in the bottom of the oven, which allows it to get too hot, too fast. You can't get the rack far enough from the bottom to keep everything from burning.
I have a double-wall aluminum cookie sheet laying in the bottom of our oven. It takes longer to preheat, but does help to diffuse some of the radiated heat from bottom of the ovven. I read that someone else had bought an unglazed, tempered ceramic tile that fit the oven bottom. That would likely work better than my cookie sheet, but would take even longer to preheat.