It's more than brachycephalic dogs though - they also looked at the extremely high instance of heart issues in Cavs, 20 times more common in Cavs than other breeds, as well as the Chiari-like Malformation skull-shape issues that Cavs have. Not just the snout shape*
MVD is a known issue in most small breeds, it’s one of the biggest killers of Chihuahuas and imo, in Cavaliers (probably with chihuahuas too), it’s high prevalence is a direct consequence of a too small gene pool from breeding for a set type.
I agree with @Littlehouseonthefairy the answer is breeding for landrace, a loose ‘type’ where dogs are a mix of breeds and there is no breeding to strict specific standards, no one top stud fathering thousands of puppies.
Chiari like malformation and Syringomyelia has been found in most small breeds with domed skulls including Chihuahua, Maltese, Griffons and others.
Only the cavalier (as I understand) has a screening scheme for it but if all toy breeds were routinely screened I suspect the true incidence would thoroughly shock people.