I'd just ask for some proof--a few test results maybe? Some old wives tales get repeated so often that it's easy to accept them as fact, with nothing to base it on.
I've been shooting the same longbow for a dozen years or so, pulling
[email protected]", and when I scaled it recently it's still right on the money. It's never had a dacron string on it, and it's my "go-to" bow--I use it for hunting, playing, shooting tournaments, etc.
I've heard that same basic thing several times over the years, but so far nobody has been able to offer any proof--or anything other than "well, so-and-so said it".
Chad