A piece of advice. Please use patch 1.03b if you play Marcus Antonius scenario, it contains several rather important fixes for this specific scenario events
Regarding Marcus Antonius from what I have read, he was a brave and great commander of small forces in the field (tactical), but strategically he was not that good, particularly in his late years, after many...conversations with Cleopatra...
. His invasion of Parthia was badly mismanaged and he was completely outsmarted by Octavianus and his generals in the civil war. So I guess his rates reflect this.
(PS: Quintus Labienus is indeed the son of Titus Labienus, first one of the most able commanders under Caesar, that then defected to Pompey when the civil war started and died at Munda. Quintus Labienus is sort of "the last of the Pompeians")