grain-free confusion - my vet said one thing, the dog food influencers say the opposite and i dont know who to trust

So my 4 year old aussie mix has been on a grain-free food since we adopted her two years ago because the previous owner was feeding it and we just... kept it going. Last week at her annual checkup i mentioned it and my vet got kind of concerned. She brought up the DCM thing and said she'd feel better if we switched to a food with grains.

But then i went down a rabbit hole and the grain-free people online are PASSIONATE. like, angry passionate. lots of posts about how the DCM study was flawed, how grain-free is actually better, how vets are influenced by the big dog food companies, etc. now i have no idea what to believe.

For context, Biscotti has no known allergies, no digestive issues, no symptoms of anything wrong. She's just on grain-free because that's what she was eating. So my question is - is there a real risk here, or is my vet being overly cautious? Has anyone actually switched from grain-free and noticed a difference either way?