Factory sheaths all seem to have several things in common, and a low price is one of them. The low price means by necessity, lesser quality cheaper leather, generally lighter weights of leather, "one shape/size fits all" design, sewing to a minimum and the use of rivets, never lined.
I sincerely doubt that anyone you could talk to at an on line vendor would be knowledgeable about leather quality generally.
Then if you did get someone to answer a question, you'd get a subjective answer influenced by their agenda.
Back to the original retention question. My answers were based on a custom fitted sheath. A generic sheath not made specifically for your specific knife and all bets are off.
Paul