Just for illustrative purposes, here’s a few of the lap dog breeds that have gone extinct over the last hundred years.
The top two images are of the Mexican Lapdog and the Russian Lapdog. Though the taxidermied specimens shown are juveniles, you can see how insanely small they were (described as being “hamster-sized”). I dunno about you, but considering wolves average around 80-100lbs, I don’t believe dogs were ever meant to be that small.
The bottom two are of the Chinese Happa who bears a striking resemblance to certain a modern breed. I can only imagine the health issues that would come with having such a flat-faced creature.
Finally, here’s an article about the health problems of brachycephalic dog breeds.