Child (English and Scottish Popular Ballads I, 185) uses the Robin Hood verse to elucidate the arrow-shooting episode in Sheath and Knife (though he later modified that interpretation: see III, 103), but does not imply any actual connection between the ballads. Do you have any evidence of a direct connection (beyond speculation based on the coincident motifs), or any to support the suggestion that Sheath and Knife is necessarily the older?

Your points are certainly interesting, but I'd like to see some external corroboration.