Good and decent yes, but his view of the Constitution was fatally flawed - as his heroic attempts to govern the South using his newfangled constitution proved to be doomed to failure.
"Died of a theory" was his own epitaph for the Confederacy.
http://www.vectorsite.net/twcw_83.html
Davis did the best he could with what he had, and like you pointed out, he thought that the Confederacy would be killed by its unwillingness to trade slavery for victory.
He was right.