One thought that occurs to me is that as you absorb more of the bass frequencies, you are changing the balance of the energy in the room. This could indeed sound brighter without and actual increase in the treble energy.
Also, I'm not an expert but the business about not being able to have too many bass traps doesn't sound quite right either.
Also, I'm not an expert but the business about not being able to have too many bass traps doesn't sound quite right either.