I agree with this. One of my favorite dogs EVER was a gorgeous, dreamboat of a Mini Aussie with a mane like a lion named Jesse... he was from a great breeder that shows & titles all of her dogs and they actually look like smaller Aussies. I practically raised him, as he came to daycare where I worked daily, and he was just spectacular in every way!
Working at the same daycare, I met more fearful, spastic Mini Aussies who were the size of large Chihuahuas... with domed heads and bug eyes. DEFINITELY mixes! I used to foster for an Aussie/BC rescue and they would routinely get in dozens of Mini Aussies from puppy mill busts. Those dogs were all very small, painfully shy and very obviously mixed. Breeders with tiny dogs, like 12" or less, are a huge red flag!
I used to want a Mini Aussie but the breed is too controversial for my taste. Unless I could get a puppy from Jesse's breeder.
I'd opt for a smaller Aussie. Many working breeders have smaller dogs, show Aussies tend to be bigger. I've met quite a few working Aussies who were 18" or less.