There are some lightweight approaches to web components. For example µce is extremely small and provides web components with no build step [1]. If you use the author's once-defined 140 byte library, you can also avoid having to bundle everything per component [2].

For those not quite ready to throw away frameworks, heresy [3] might be more up their alley, or if you're not as set on production readiness yet, check out my own barleytea.js [4] which is written in a little over 300 SLOC and has zero dependencies or necessary build steps.

I guess my point is, there is a good variety of microframeworks out there striving to meet this need.

[1] https://github.com/WebReflection/uce [2] https://github.com/WebReflection/once-defined [3] https://github.com/WebReflection/heresy [4] https://andrewfulrich.gitlab.io/barleytea/