The old UI was not "pro", it was "ancient". "Old reliable" maybe. If that's your reason, then it's not a very good one. If the product is missing all the features you need, that's a much better reason.
I don't think anyone wishes OS X still looked like 10.1...
OMG, that little boy on the photo of the Preview app icon is still the same! I wonder who he is and how he's doing now!