Would have liked to see them use 4.1.0 as you stated in a comment but oh well.
I have to agree with their perspective though: you don't use release candidates for benchmarking, only shipping software.
Anyway, why is it that their grid is faster? I thought the v4 grid in ExtJS was supposed to be engineered for better performance?
It turns out to be a bad test also. Other frameworks as the number of rows get larger the speed stays pretty flat? Sounds like they are buffering then and the example they have of Ext JS is not a buffering one so of course the performance of Ext JS is going to be so bad.
I checked their code, and I didn't notice anything about buffered views.
But, it's still relevant, because they just implemented the grid like the Sencha examples recommend. I literally couldn't figure out how to do buffered grid views in ExtJS 4 (I only use v3 professionally) with 15 minutes of browsing the documentation. That's a problem with ExtJS and its documentation, not a problem with the benchmark.
Have you see the buffered grid example? Basically the example in RC2 loads 5,000 records into the store and between the grid and the store it only shows a certain amount at a time.