I don't think you could possibly say that onions do NOT go in meatballs.
It is totally a taste preference!
Maybe I don't make them that way.....but who is to say that it is wrong? It is just what we are used to and prefer.
My Northern Italian family always put onions in their meatballs, NEVER in the sauce. And we would NEVER call it gravy! LOL
My BF is Sicilian and always used onions as well, both in the meatballs and the sauce.
All of them use veal...I would NEVER eat veal! I combo beef and pork.
I NEVER use onions! LOL My kids would spit them out no matter how small I chopped them.
I now use ricotta (saw it on Top Chef).
Our meatballs are always pan fried first in a cast iron skillet...never baked or put raw in the sauce.
Meatballs are as varied as the day is long.
I would never order meatballs or cheesecakes since I love my own...but I order a lot of food from Q and have been mostly very pleased.
You have to remember, some people do not cook, don't know how to cook or don't WANT to cook! Having sources such as Q or Swann's are helpful in their lives.
I don't judge what others choose to spend.