Underscore makes me wonder if people really understand JS.
What do you mean by this? Typical _.js users don't really understand javascript?
I ask because I feel like _.js is a fantastic library that I've been using in almost every project of mine since first trying it out. I've really grown to like it, but am interested in what you mean by your comment.
I don't know the grandparents reasoning for the statement but if I where to assume, it would be that many of the popular implementations support much of the functionality natively. If which it may be that the grandparent is not considering the case that many use underscore as a polyfill to support such functionality on a broader array of clients that may or may not support the functionality of underscore natively. The grandparent may have other reasoning but that would be my first guess.