Am I making a mistake going with a heavier, thicker bumper?

Exactly GDEtrailer, a bumper is for protecting the trailer from minor incursions. Had a person in Yellowstone run into the back of my TH TT. With the heavy metal that the hinges are mounted to did zero damage to my trailer and put a dent into the hood of the Volkswagen.

If you were to hit a minor object at low speed like a tree or power pole you would have some protection. Otherwise if you damage aluminum siding or fiberglass you would have to remove the whole back side of the trailer to repair.