JSPM is slow to build but I don't see much utility in building during development when on-the-fly transpilation can be used instead.

In terms of using JSPM to create builds for production, it seems significantly easier to setup than the equivalent using gulp, browserify, webpack.

Easier than Webpack? I dunno about that. I have major gripes about webpack, but being difficult to set up is not one of them.

The problem with Webpack IMO is that it kinda feels like Grunt sometimes where you find yourself editing a giant nested config. But it is by far the most flexible tool for the job and setting it up without all the fancy stuff is pretty straightforward.