wpgraft never reads Divi’s data. There is no exporter, no importer and no shortcode translator anywhere in this, by design, because those are the parts that break. wpgraft reads the page as your browser rendered it: the real elements and the real computed styles on each one, at every breakpoint you ask for. It then rebuilds that as Gutenberg’s own native elements, with the styles written into Gutenberg’s own fields. Nothing that arrives depends on Divi still existing.
Divi pages are held together by Divi: its shortcodes or its blocks, plus a page-specific stylesheet and a set of defaults that repaint everything on the page. Moving to core blocks means leaving all of that behind, and wpgraft does it by reading what Divi drew rather than what Divi stored. Divi 4 and Divi 5 pages both work as a source.