I prefer to get my dogs from one-off breeders who have researched the stud and breeding.
Unfortunately, these are few and far between
The commitment required to research health, temperament, and invest the time and money required to produce a healthy litter is very significant - and in my experience, someone who "has a one-off litter" is less likely to be prepared to make the sacrifices required than a dedicated hobbyist who is committed to welfare and improvement and has extensive experience and knowledge based on their involvement in activities and network of the breed.
IMO, your assumption that breeders who have "lots of dogs" don't focus on the puppies so much is a generalisation.......
an ethical hobby breeder will not have numerous litters at once, and will ensure that they give the puppies the time and socialisation experiences they need, but will often have a number of dogs