Please observe Grimes at Cochella: https://www.youtube.com/watch?v=E01QyNHBpcc
(yes, she reacted suboptimally, just don't think it's fair to use here)
Grimes is a performance artist who dabbled in music. She’s not a musician. Imogen Heap is a musician.
Mixing vinyl well is definitely an impressive skill but I (and I suspect the vast majority of people) don't care at all about how people are mixing tracks (until it's to the detriment of the music). Most people care about what makes them dance and/or feel something.
I have seen some unbelievable performances by matching wizards who added a whole other level to the performance with their skills.
The set itself was different because there would not have been a way to slice and dice the set together without those skills.
Really no different than a virtuoso performance on any other instrument.
I mean, there clearly is if you ever try teaching a beginner to beatmix (whether vinyl or digital). I don't disagree with your other points.
Put any sync button DJ in front of a proper CDJ setup, give them a couple of hours to practice and they will be able to pull off a set.
Most importantly: it is the least important part of the job. Nobody in the crowd gives a shit about whether or not you're using the sync button, it makes no difference to them. They're not there to stare at you, most of the time they can't even see what you're doing.