I know what you mean, I just dunno if the question actually make much sense when you break it down. The closer to just JS, the smaller the framework’s API, the more boilerplate, the harder you’ll find it as a beginner.
React is probably the closest out of the current popular frameworks. Its entire API is just a set of functions for efficiently updating a tree structure (just a JS object) representing your app; you then use the ReactDOM library to take that and spit out HTML. JSX is just a way of writing JS objects that looks like HTML. This is possibly one of the reasons people find it hard; it doesn’t really do much apart from that, it takes craploads of boilerplate to do some stuff that seems like it should be simple.
Backbone was an older thing, allows MVC style apps, takes loads of boilerplate. Marionette is the normal view layer library used with it I guess.
Mithril is pretty close to vanilla I guess? Riot? Hyperapp?
Just looking at small frameworks that don’t do a lot on their own.