Changing the following settings improves the markdown export for the purposes of importing into roam:
(setq org-export-with-toc nil) ; remove TOC and anchors
(setq org-export-with-special-strings nil) ; do not encode '--' as '–'
(setq org-export-headline-levels 0) ; export headlines using lists, not '#', this preserves indentation when pasting into roam