The problem with your point is that it assumes users' are using Chrome because of its rendering speed. I don't think that's the case.
But I am assuming that a browser offering a gigantic leap in UX through native-like rendering performance will entice web app developers to recommend that browser over others, because it's nigh impossible to build a consistently 60fps non trivial app with native-like interactions and transitions on the web today, while Servo and Webrender aim to make 60fps on the web the norm rather than the exception.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1347543 [2] https://bugzilla.mozilla.org/show_bug.cgi?id=1054016