The planned matchup against the BC fleet was put on hold for the long game until Barbarossa gets here. However, the Marine did prove useless in that game, as the Tiger’s Eye took it out first try.
I do think Marines can be neat counters to Barbary ships because of how poor Barbary cannons can be, but they’re still way too expensive and like you said, since the Barbary Corsairs can still explore and leave as long as it has 3+ masts or an explorer it won’t be in any real danger. I think they should’ve been able to shoot twice on land, like longships sorta.