I've been using Vagrant since the early days. While I have to admit I've spent zero time in the Vagrant source and I'm sure your assessment is accurate, I'm not sure how much I really care that it might be java-ish or bloated or not well written. I like well written code as much as the next guy. But I'm not deploying Vagrant to my production machines to be accessed by millions of users where I need to squeeze a few milliseconds out and I'm not building on top of vagrant as a framework. I use it behind the scenes as a tool to save me time and bootstraps my development servers. And it does that well. You don't need to maintain the internals, which means you can focus on your actual business, which I don't think is writing provisioning tools :)

Edited for spelling