That’s bs. No matter how good your theming system is, it can’t fix a bunch of things. Even something as basic as text being shown against a background with not enough contrast.

Theming has been known to cause issues on literally every DE. You can’t stop people from theming poorly.

And random devs shouldn’t be on the hook for third party themes that cause issues. Nor should they be expected to drop everything and investigate bugs in somebody else’s theme project. That stuff should be reported to the theme developer.