There is no such thing as any potential trope being too common to make an actual trope. Plots, Characters, and Conflict are tropes, and literally no proper story can be told without them (whatever form they take). That means that, by necessity, they have 100% use on any work that tells a story. If those aren't too common, then no other trope can be too common. Finally, People Sit on Chairs should not be used just because a trope is common. That's about lack of purpose, not too high a frequency. Something could be rare and still have no purpose. Compare/Contrast Too Rare to Trope and Not a Trope.