Cats have only been intentionally bred for about 150 years (less than 5% of domesticated cats are purebred or have any significant percentage of a pure breed), so we are just seeing the beginning of the manmade horror show that is irresponsible breeding with cats. It's already starting; many cat breeds that look physically normal or healthy are more likely to have certain health issues. You basically will not find a purebred cat at a shelter, so if you want a certain breed it is imperative to buy from a good breeder who tests their cats for genetic health issues.
The ragdoll, prone to hypertrophic cardiomyopathy (basically the heart stops pumping blood effectively, an incurable disease), bladder stones (already a big risk for cats on a kibble diet), and joint issues (due to larger size). Created in the 1960s. Many cats in shelters are advertised as Ragdolls but are actually just colorpoint longhaired "mutts."
Persians have already been discussed because of their squished faces, but even Persians with a more prominent muzzle are unhealthy, with
about 2/3 of Persians suffering from some chronic health disorder. Has kinda been around since the 1600s, but the modern Persian cat seems to be genetically distinct from the Persians discussed in literature from that time period, and the modern Persian has only been around since 1950.
A purebred Siamese, note the weird body proportions. Like the Persian, the modern Siamese looks quite different from the Siamese cat described in ancient Thai manuscripts and has only been around since the 80s or so. Prone to tumors and eye problems (crossed eyes or blindness). Lots of people think any colorpoint shorthair is Siamese.
A true Russian Blue. Looks like any other grey cat, just with nice green eyes. Prone to GI and urinary issues, as well as ear infections.
My point is that we have plenty of time for humans to fuck up cats even further.
As far as "adopt don't shop," I've grown sour on shelters. It's worse with dogs, but shelters will gloss over an animal's behavioral problems or advertise them as the incorrect breed to try to get people to adopt. Worse with dogs having a potentially aggressive history, but cats can have behavioral (pissing everywhere, pica) or health issues that shelters will sugarcoat. Rescues are also getting choosier, with some who refused to adopt to me because I own a reptile and others wanting proof I owned my house and wasn't renting it. I thought they were overflowing with animals, but it's like pulling teeth to get them to respond to messages, let alone allow you to meet their cats.
I have a Maine Coon x domestic shorthair from an iffy breeder who let her TICA-registered Mane Coon around her unspayed domestic shorthair. So far the best kitten I've ever had, and I'm unsure if that's due to the half MC or just her individual personality. Way less fuss and muss than dealing with a shelter.