Roy Moore's speaking ability or inability did not cost him the election. Unprovable accusations and subsequent abandonment and condemnation by his "allies" are what cost the election.
Some Accusations against Trump in 2016 election:
He is a liberal who contributes to democrats.
He never served in military.
He boasted about how easy it was to grope women.
He was pro-abortion before he was pro-life.
He had zero elective experience.
He had 3 marriages.
He never published his tax returns.
blah blah blah....
But Trump overcame the fierce opposition by 16 establishment candidates with ability to keep massive audiences eating out of his hand with rally speeches. He counter-punched every attack with gusto. Moore could not and did not.