My mom left me a home packed to the gills. She was the most empathetic person I ever knew, to the point of paralysis. She purchased things to be gifts for family, to show she had value. So yes, if someone is hoarding to try and have value, and you tell them they have zero value, they will get defensive. It might be you that is controlling and lacking empathy. And I don't think it's obsessive control they have but rather obsessive lack of control so they purchase these things as protection/armor.

If you had empathy, you would see that attacking their hoarding is both devaluing them and trying to remove what they perceive as safety so yeah, they are going to respond as such. If I pushed hard for you to give away your bank account and that you are crazy for having it you would probably push back in the same way. Maybe approach from empathy instead of judgement and you'd get a better response.