Allow me to float ZephJS at you as an example of a Web Component framework with a bundling tool to do what you describe. Simplifies everything about building Web Components.

Introduction: https://gist.github.com/arei/8083a6270e704b830c68a2020f3e5e3...

Bundling specifically: https://github.com/awesomeeng/zephjs/blob/master/docs/Compon...