That's why Locarno wouldn't have worked. A good character is a well-rounded, dynamic character. Tom Paris was a more-than-competent pilot, he made a good medic (even before receiving extra training from the Doctor), he had a conscience, he had a strong sense of duty and loyalty, and he knew how to have fun. I can't imagine Locarno goofing around with Harry in the Captain Proton program. I can't even imagine Locarno and Harry even being friends. I certainly can't imagine Locarno as someone B'Elanna would be friends with, never mind eventually marrying.