While that's the Supreme Court's post hoc interpretation, you have to admit it finds little support in either the text or history of those amendments. It's unlikely the states that ratified those amendments realized they were giving up the right to set local standards of how to treat the accused, etc.
I would base minimum federal standards of local criminal justice and election conduct and etc. on the commerce clause, if it were up to me. Not meeting such standards amounts to claiming you should be allowed to build highways that won't accept heavy trucks. It would make it hard to do business nationally.
But, yeah, Reconstruction and subsequent events shaped those Amendments.
