Unless you are the rare NFL team that miraculously has two NFL QB's on it's roster (I'm looking at you 2017 Eagles) then it doesn't matter a bit who your backup QB is. The best you can hope for is that your backup can fill in for a few plays here and there. A half. Maybe a game or two. After that, you're just plain sunk.
Past that, you might as well have some young guys and find out what they have or don't have. There are NFL teams out there without a single NFL starting caliber QB on the roster. We're lucky to have one.