>Perhaps nostalgia and the principle of KISS (and a few others) is clouding my judgement here, after all, frameworks are made for a reason. But it's difficult to imagine a new engineer having any more difficulty with vanilla than learning framework after framework.

I feel the same way. React and Angular (well an earlier version of Angular) were made prior to ES2015 being mainstream, so I do think they made sense to use when they were initially created. Since then, I've become burned out from the constant churn of new frontend frameworks to learn. Even within the world of React, there's different ways of writing components, and different state managers.