In Ovid's version, Perseus does *not* use the head of Medusa to kill the sea monster. After flying up and stabbing it in the shoulder, he then swoops down to a rock and stabs it repeatedly: "His left hand on a ridge, and with his sword stabbed time and time again the monster's groin" (IV.732 -- 33). Immediately after, Andromeda is released and they marry. This conflicts with the analysis, also, that he's not brave or heroic enough to face the creature using his own arms rather than just the Gorgon's head.
In David Raeburn's translation of Ovid's Metamorphoses, Pelias' daughters give him a bunch of gashes with their swords (ll. 338-41), and then Medea deals the final blow by slitting his throat (ll. 348-9).
Aeneas was not the founder of Rome. He founded the city of Lavinium, named after his second wife Lavinia. His prophecy told him that he would found a city where Rome would be later on in time. Rome was founded by Romulus, a descendent of Aeneas.