I still maintain that MooTools was the superior system over jQuery.
jQuery won the war, in the end, because it catered to the 'get it up and running now' crowd over the 'do it right' crowd. It was always easier to understand off the bat, especially if you aren't a trained developer, while MooTools makes for a more long lasting, quality codebase.
No jQuery won the war because it fit with what JavaScript does in the browser while MooTools lost because it was part of the Java/OOP fad of "Well it has a new keyword so let's extend classes with it!" that has (thankfully) been rendered to the dustbin of history where it belongs.
jQuery won the war, in the end, because it catered to the 'get it up and running now' crowd over the 'do it right' crowd. It was always easier to understand off the bat, especially if you aren't a trained developer, while MooTools makes for a more long lasting, quality codebase.