The link you provided is out of date. Here is the latest version:
http://jsperf.com/class-vs-data-attribute-selector-performance/21
To your point, attribute selectors are relatively slower, but I wouldn’t say slow. Looking at the benchmarks, they can still complete thousands if not tens of thousands of times per second.
Selector execution is rarely the bottleneck of a web app, since they typically only run once for setup or upon some user action. Unless you’re spamming selectors non-stop (not a good idea) then the extra milliseconds won’t amount to much.