MK had 40 million extra guests per year in 2019 than it did 10 years earlier in 2009. Comparing how thing are now to just 10 years ago, let alone 30, is literally incomparable.
Without any sort of FP, the park reached a tipping point in which there were more people than all the rides and attractions together could handle. MK was a victim of its own success.
FP+ was developed to deal with that excess demand, it didn't create it. People can argue with how well it did or didn't deal with that mess.
But one thing's for certain, without FP, there'd still by hours long waits at many of the attractions because there's more people in the parks than that attractions can process.
Variations of FP won't fix the overcrowding. Adding capacity, or making the other underutilized parks more attractive, or capping attendance with a hard limit (park reservation) or with carrot/stick (higher prices) are the only solutions to long lines.