Doubtless that is true. My grandma isn't in any records I've found anywhere, and I have her letter of acceptance by her local chapter. That was a big deal in small towns. I was never interested. I only have two or three who fought, and would have a hard time proving any of them with the exactitude they should require. I think their records can be an aid if you do more independent research. A mistake can get replicated indefinitely.
DAR records from a couple generations ago are sometimes slipshod. I also had some folks join on an ancestor of mine that has since been discredited. No more memberships can be based on that individual.
Today, with digital records, etc. DAR is a lot more picky. You can no longer prove descendency based on county book sketches, etc. They want to see wills and other court documents regarding birth, marriage, death; bibles; sometimes graves, but they want to see something set in stone as it were. Many of these older family lines have been discredited.
I agree with you mistakes get replicated all the time.
I did my own geneology search as well and found many people(thousands) claiming my Grandfather was related. As I filtered out their results based on KNOWING my cousins, I found they were related to another “Bentley” that came to the United States in the late 1800’s form a completely different European country!
So, it does happen a lot. People want so badly to romanticize their family past that they just ignore the less grand results.