I would hardly say he shredded the competition, given that he also made a video about how janky MuseScore 3 was, and then was given the opportunity to fix it… and did. And he included a pisstake about MuseScore in the bit which included a pisstake of Dorico, Sibelius and Finale.
As for his design; actually I think he more than most has a history of producing excellent design. His Leland font is superb, if you read his design thoughts about Audacity they make it easier to use and understand, and MuseScore 4 is groundbreaking in terms of open source software.
I’m a big user of open source software. I have bought precisely three pieces of software in my life not counting Windows which came with the computers I have bought. They are Sibelius 6, because it was the best piece of software available at the time (and my Dad taught the Finn brothers Physics and approved of them), Dorico because Sibelius 7/8 was an unintuative disaster area which used icons from the Encarta Encyclopaedia from 1992, and Dorico was much, much better, and DesignaKnit, because it was the only practical solution at the time.
I love things like FreeCad and LibreOffice, but you universally have to put up with nonsense that you wouldn’t have to with proprietary software because it is basically designed by committee.
MuseScore (at least version 4, and to an extent 3.6) looks, feels and acts like a piece of proper high end scoring software - certainly 4 has been much better than Sib 8 or Finale ever since I started playing with the alpha release, and it is free. Utterly, GPL licenced, for ever and ever and ever, free. Can you name even one piece of GPL software which comes even the tiniest bit close to the standard of MuseScore 4? I very much doubt it.
So yeah, I do rate Keary’s design. I’d say him and Daniel’s Making Notes blog are the two most impressive pieces of notation design philosophy I have come across.
Interestingly, the MuseScore forum folks tend not to get snotty about the Dorico team, or call him “Daniel S**tbury” or any other nonsense. Some are annoying in other ways of course, but ad hominem attacks are rarer.