You are correct. I believe performance is a must but not what is most important. You could see other interesting features like debugging experience in the framework. Server-side rendering I believe is also a really powerful feature.
http://jsblocks.com/learn/introduction-why-jsblocks#debugging-experience
Additionally, I have been developing jsblocks for the past two years and I think that it has a lot of features to build complete applications. However, you could give an example of what jsblocks does not have that other framework has. :)
For starters, right now I can only see a few true frameworks out there - Angular and probably Ember, the rest, like backbone, react and many other so called "frameworks" are only libraries. JSBlocks as I see it from documentation is also only a library, far from true framework.
Now the problem with libraries is that they offer too much freedom and with all that freedom comes loads of different approaches that are difficult to follow or even impossible at later stages... If you are willing to build your own framework out of library that might be fine, but if you want to work in a team and try to recruit members that already know a framework that might get tough and it will be even more difficult when problems stars rising with your "framework" and no answers could be found on stackoverflow or other resources...
Anyways, I believe that someone can compare full frameworks like angular only with another full framework otherwise it might be really unfair comparisement.