Thanks for the review! You touched on it, but I think the key difference is that Pup is a boilerplate, while Vulcan is a framework. In other words the way Vulcan is architectured, you can easily add/remove/update packages at any point in your app’s lifetime, whereas with a boilerplate you’re kind of on your own after you start. I think they both have their pros and cons, like you pointed out.
(I also think Vulcan and Pup might differ when it comes to actual features, but I’m not familiar enough with Pup to really say)