I think the answer to your question is: Both. My husband was raised in a hoarded home that was really bad. I was raised in a clean, but lived in home. We always cleaned the house and dusted and vacuumed, but my mom was not obsessive about it She had 6 kids and she knew the house was never going to be perfect, but it was always picked up and clean. When my husband Mark and I started talking marriage I let him know right away that I could not live in a hoarded home and that if there was any part of him that was associated with the hoard in his mother's home, we may have a problem. Mark said he was not a hoarder and we have been married over 20 years and we have a perfectly clean house. The only hoarding tendency I see in my husband is books. He loves to read and he has a lot of books, but we have bookshelves and I told him as long as he keeps them on the shelves that is fine with me. He reads them then he sells them at a store that sells used books and things are just fine.
Mark has a brother, Peter, who "inherited" his family hoarding situation. I do feel like hoarding is a mental disorder and one that needs a lot of help. We have had family members reach out to help Peter, but with little success. He filled up an entire house and had to move into another house and he already has that one almost full. He takes home anything and everything and he gets rid of very little. He needs help, but he doesn't see it as a problem, and if someone cannot see that they need help they will never accept the help and get better.
My mother-in-law on the other hand has had to move from her hoarded home to an assisted living facility where she and my father-in-law are in a small apartment. She has had to change her ways, The facility has regular inspections and she has to keep their apartment clean and hoard free or they cannot continue to live there. She is doing a great job and I am proud of the huge strides she has made in just two years. I think there is hope for everyone, they just need to be able to accept the help to move forward. Good luck to you and your family.