First of all, shaming someone for getting a dog from a backyard breeder is inappropriate. Everyone starts somewhere, and most of us, when we started, didn't know the difference between good or bad breeders. Unless someone is lucky enough to have a friend who is immersed in the dog world, their first dog will likely be from a byb.
I think there are levels of 'ethics' in breeding. Puppy mill - unethical. Backyard breeder who does no health testing, doesn't care where their puppies end up, don't follow up on their puppies to make sure they aren't producing dogs with faults - unethical. Hobby breeder who knows a bit about the breed, maybe does some but not all health tests, cares about their puppies and follows up on them - not 100% ethical, but this is where many breeders fall and I'm not willing to call them 'bad' breeders, but they aren't doing everything they can. And then there are ethical breeders - all health tests, right of first refusal, health guarantee, knows the lines of their dogs, chooses a sire/dam who complements their dog well, screens buyers, usually titles their dogs, etc.
DCM is a disease that can be tested for. So OP, I have to question whether the breeder of your first dog did this testing on their lines. While DCM can remain hidden for generations, it's pretty rare for a dog to have DCM from lines that are fully tested, both breeding and non-breeding dogs. Many breeders *say* that their dogs are 'health tested', but what that actually means is that a vet has looked at the dog and said 'this dog is healthy'. REAL health testing comes with OFA numbers that you can look up on the OFA website to verify the test results. OFA paperwork can be (and is frequently) faked, so those numbers and looking them up on the website are really important.
The way I look at breeding (and I wish more people did) is this - you're paying for the NEXT litter that breeder is going to produce. If you don't feel comfortable with that breeder producing another litter because this litter is in bad shape or not being cared for, you're only paying for MORE puppies to suffer.
I want to pay breeders to produce more litters who are active in the breed, producing good, healthy, moderate dogs who are being titled (in whatever), who tracks their lines, who will always take the puppy back if something happens, who cares what happens to the dogs they produce, etc. Buying a dog from a healthy line is in no way a guarantee of health, but it's the next best thing you're going to get when you're dealing with living animals.
In Danes, that type of puppy comes with a pretty large price tag. $1.5-3K is average. I understand that many people cannot afford that type of financial commitment, and that rescues won't adopt to many people for very asinine reasons, which is why I'm not willing to condemn the hobby breeders out there who are mostly doing the right things and who are providing companions for the absolutely massive companion puppy market. There's no way all of the really amazing breeders can keep up with demand, so there needs to be a person between the puppy mills and reputable breeders who are doing it mostly okay. And to me, that's where it sounds like you got your dog, and I see nothing wrong with that.