Achilles has the skill.
Cap has the limited superhuman strength.
The shield in film has proven that force against it doesn't mean much.
In other words Movie Cap's shield doesn't adsorb all damage.
In actuality the film shield just doesn't break under pressure.
But such restrictions don't really apply to Achilles, but considering Cap destroyed chunks of a SHIELD hover mobile. It proves he has strength behind his throws. Strength Achilles doesn't have.
In this setting Achilles falls to the floor once Cap throws his shield against him. Cap catches his shield and moves in and repeats.
A vibranium shield, will repel a vibranium shield. Achilles has the reaction and ability to see attacks before they happen.
His shield stopped Thor's hammer, I'd say it absorbs damage beyond anything else.
His strength was shown to be above human levels as Hector stated that he had never seen a man throw a spear that far before.
Considering they both have identical shields and Achilles knows how to use a sword and shield beyond Cap has shown in a sword and shield fight, that will give him the advantage over Cap.