Since XSL-FO was built with CSS hounding it to use the same semantics,
In a large number of cases the xsl-fo syntax would provide the XCSS above?

Ahem, not quite. In the XSLT+XSLFO combo, XSLT got the selector
part (match="...") and various methods to centralize bundles of
style declarationss (within templates, attribute-sets). This
is lacking in XSLFO, where all style attributes are expanded
on every element, except inherited properties.
Well, I should have mentioned I meant CSS in <style> tags or
linked rather than in style="" attributes. There is no XML
syntax for this kind of "style repository".