Yeah, I believe some ex-Googlers even claimed that writing Gmail was simply impossible at that time with ordinary JS, and the abstraction behind GWT was an absolute necessity (though maybe the frontend part was not all that important - closure compiler is still alive though)
On the other hand, gwt did not gain much traction, and the majority of frontend developers disliked it (granted, they do prefer javascript+css rather than coding the frontend via gwt widgets).