First of all I want to say I'm sorry your heart is breaking.
Your little man is now waiting at the Rainbow Bridge for you.
Second, I really think the story is about the breeder that let this tiny puppy go home at 9-10 weeks old! I have had dams that still let their puppies nurse until over 12 weeks and if they want to I let them. Weaning is the hardest time for a breeder and the one you bought from handed that responsibility off to you and your Gonzo suffered the consequences. It would be during the weaning transition a reputable breeder would see symptoms of problems or at the very least allow them to get big enough for their little systems to be able to eat puppy food. If you focus on the size issue, you do a disservice to those healthy little yorkies that have no physical illnesses due to their size and the breeders that keep them until they are really ready to go. I have a 5 1/2 month old that is 2.9 lbs and very healthy. Her sire is 3.5 lbs, 10 1/2 yrs old and still excited and energetic to sire puppies. You wouldn't know he was older by how he acts and someone picked him up the other day and said wow, how much does this one weigh? 5 lbs? He's a solid little dog (the one in my avatar) and I describe his build like a tonka truck. The little girl I was just talking about has not had one problem but I've kept her longer to make sure of that.
I am sure your heart is hurting and you want to lash out and bring justice and meaning to your loss but please take a moment to step back and see the whole picture.
Sorry this is so long.