So I've been playing on an alt knight, and glanced at the supply depot because why not. I noticed that all the 5* guns were showing up despite only being a defender rank.
Swords, bombs, helmets, armors, and shields all only show the appropriate rank, however guns are able to be seen and purchased before reaching defender elite.
Additionally the in-game bug report function seems to not be able to send in reports, so that's something that might need some looking into as well.
I've had the same problem as well! Only on the guns tab does all the equipment appear, even those beyond my knight's rank.