this, in itself is not a bug, however, any code relying on the @material-ui/styles instead of the styles export from mui/core will break. why not just add a default style so things don't needlessly break? the package is already 400kb its not like it matters... not breaking things trumps some arbitrary size constraint
@material-ui/styles is completely independent from @material-ui/core. A default theme is added in the exported style functions in core.
belief isn't reality
https://next.material-ui.com/customization/default-theme/#material-ui-core-styles-vs-material-ui-styles