They pulled in more revenue than the average McDonald's and 3x more than Pizza Hut.
It does seem like the concept has always struggled to be cost-efficient but I don't know that rapid growth was a bad indicator on its own.
It's also probably worth keeping in mind that some of those restaurants may have been franchised. When a franchisor sells a franchise license to a local franchisee, the local franchisee bears most of the risk.
https://www.youtube.com/watch?v=BbI3zOm2BkE
Skip ahead to 7:20
They pulled in more revenue than the average McDonald's and 3x more than Pizza Hut.
It does seem like the concept has always struggled to be cost-efficient but I don't know that rapid growth was a bad indicator on its own.
It's also probably worth keeping in mind that some of those restaurants may have been franchised. When a franchisor sells a franchise license to a local franchisee, the local franchisee bears most of the risk.