I'd argue it's pretty important for working dogs too, especially ones that require specific temperaments for their jobs like border collies, livestock guardian dogs, and pointers.
Our dog had a mysterious bowel issue that wasn’t treating with the standard food change methods. Vet did a dna and found he’s more chihuahua than Australian Shepherd despite being dead on shepherd by appearance. Then more or less immediately they worked out his issue since chis have specific bowel issues that don’t usually happen in aussies.
So it does have valid uses for assisting diagnostic medicine
Similarly, we have two Danes and our second one is a bit smaller (only 90 lbs) and has slightly different facial structure than what we are used to seeing. So we got her DNA analyzed-and she's 100% Dane. It helps to know that since we now can have clearer expectations of what kinds of needs she will have as she ages.
Anyone can lie and make fake paperwork. DNA is just that second check to have a much better read on the truth (assuming they don’t mix up the samples).
Honestly, I’m not a breeder or a dog enthusiast though. However, I do love my shibas even if they may not exactly be pure bred.
Litter loading is a thing. People buy a dog but it's swapped for a cheaper or non pedigree. DNA testing is done for puppies to verify that they are what they're supposed to be and AKC requires it sometimes.