My friend told me dry food is like junk for cats, explaination as to why?

I was at a friends house just the other day. She feeds her 3 senior cats and 2 kittens cats a staple of canned food + frozen and thawed raw meats once or twice a week. I asked her why she didn't feed her cat any dry and she told me is was junk food for cats. She actually has a little treat jar with some friskies dry food which she considers to be treats and rewards for good behavior and not a staple diet "by an stretch of the imagination" she quoted. She didn't really explain to my why dry food is bad. Now it has me thinking since my 2 cats are eating cat chow with CANNED as the treat right now. IDK my friend is pretty knowledgable and her cat is 17(been living with her for 9 years)and still going, so I'm pretty sure she's right. I only want the best for them. If it is true canned is best, I would be really interested to learn about why and what problems it could lead to. thanks!