When Chrome first came out in 2008, it was noticeably faster than any competitors. Users with only moderate tech knowledge were switching in droves because it was faster. Part of this was that it had a process-per-tab model properly making use of multi core CPUs for the first time, but much of it was because V8 was fast.

The gap is not so big these days. JavaScriptCore, Spidermonkey, and V8 are all competent.