There is no possible way for you to eat a Wendy's burger and BK burger and tell me it's the same quality of beef. 100% beef does not mean it's quality. It's where they get the meat from. If they get it from farmers that feed their cattle crap, that's the way the meat will come out. It's still 100% beef.
I like Wendy's because IMO they haven't changed much over the years although some would argue with me on that point. The reason their double burger combo is more expensive than BKs is the quality of beef. As for their fries, most all FF restaurants are the same. That's why if I do go to BK, I get their onion rings instead.