I've always found that quote to be particularly douchey. Then again, I do think that Dijkstra's contributions to CS were more important than Kay's, too, but I suspect that I might not be in the majority there...
Dijkstra worked in Computer Science. And the relevant quote there is that "Computer Science is no more about computers, than Astronomy is about telescopes.”
Dr. Kay did phenomenally important work with computers and programming. It’s important in its own right. Either of us could say that we prefer to dwell on the ramifications of one or the other.
I think it’s safe to say that if you took either of their contributions away outright, our world in 2015 would be much poorer for it.
Now if you want a good Dr. Kay quote, “Programming is a Pop Culture” has to be high on the list. I think he’s deeply right about that, but being right doesn’t in any way tarnish the nano-Dijkstras associated with damning the entire field.
I agree that they both did very important contributions, and that there's probably no way to compare their magnitude, so it comes down to personal interpretation, there's no argument there. Still, I believe the arrogance comment by Kay was douchey :)
"He was the first to make the claim that programming is so inherently complex that (...)"
Meanwhile Alan Kay had 12 year old kids making computer games (videos on Web Archive).
Dijkstra contributed algorithms. In that sense he contributed as a mathematician. That doesn't diminish what he did. But it does not compare with what Alan Kay did for the sum of these two parts: computers, and people.
Dijkstra was correct in saying that you don't even need a computer to do "Computer Science," all you need is a pencil, paper, and a mental model of what you're trying to do given computer constraints.
Dijkstra more theoretical; Kay more hands-on.
I think BOTH are necessary, or at least important.
If Dijkstra is so awesome someone should write a Wikipedia article with more important achievements and less medals.
Instead of waiting for someone to write on the wiki, you could go out there and google a bit.
Very briefly: he made major contributions to compiler and OS design (including the first Algol compiler and a whole OS, the THE OS), devised two fundamental graph algorithms (shortest path and spanning tree), and spearheaded making programming into a serious discipline rooted in maths (along the way pretty much giving birth to structured programming).
He also wrote (longhand!) over a thousand essays on CS and related topics, which are (as far as I've read, and I've read quite a few) all a joy to read.
You can start here: http://amturing.acm.org/award_winners/dijkstra_1053701.cfm and here: http://www.cs.utexas.edu/users/EWD/