It is surprising what can bother you. In this case the tower the brothers explore bothers me on a very basic level. Structures have to be built out of available materials, you can’t just scale up regular materials to achieve the same affect without some other built in reason. Especially when you contrast it with the remains of the giant battlefield, there weapons are clearly made out of regular sized trees and materials. We definitely know that giants are around, but we don’t see any giant trees growing anywhere.
It feels to me like seeing tiny people from a series like the Borrowers living in and using items and materials that were clearly custom made and sized to fit them. There simply isn’t the justification for it in the story and I find it surprisingly immersion breaking.