Apple very rarely admits mistakes. The fact they're rolling back some of the extremeness in Liquid Glass and actively mentioned in the keynote that they very seriously took the user feedback shows just how bad it was, at least initially.
Excep every time they do a big redesign like this. This happened when they moved away from skeuomorphism in iOS7(?) and then backpedalled hard in the following revision because of negative user feedback. Similar thing happened when they presented the reinvented Safari (I do't think that one even survived through betas). And it is happening now.