Yeah, Shanks should've been a gray (but ultimately good) character willing to play ball, for his own means and agenda. Say like Aokiji for example. But too complicated for Oda to execute I guess, plus Oda's self insert.
and it would have been totally in line with what Sengoku said at the end of MF to stop the war
no need for a Shanks copy to make it works
But yeah Oda didn’t want to touch to his golden boy