I guarantee you that's not the case.Let say that look at 25 clients shooting ELD-X and 25 clients shooting something else.
The outfitter is saying that he has seen the ELD-X group loose more animals that the other group.
Is it a perfect, statistcally valid experiment? Probably not.
Should it be completely dismissed as irrelevant? Also probably not...
Go call 50 outfitters and ask them what cartridge they recommend for their elk hunters. That'll tell you everything you need to know about how trustworthy an outfitters' knowledge is on anything ballistics related.