My guess is the parks were not nearly as crowded as they are now. All new entertainment options, more dining options, so many more people in the parks blogging, vlogging, more people staying on-site, etc.. Disney's expansion in the Eisner era was massive. You no longer had just 2 parks and the Vacation Village (now Disney Springs). The massive growth brought massive crowds and that meant so many more people waiting in incredibly long lines and not using the time more (Disney) wisely, like shopping and eating. FP changed all that.
Not really. The parks are busier overall, but they still operated just fine on packed days for 30+ years. FP wasn't rolled out until 1999 and by then all four parks were in operation. Even then, it was only used at E-Tickets, for the most part, until MDE came along more than a decade later.