If you think that anything Lando did in the original trilogy precluded him being pansexual, you're nuts. All we know is that he flirts with Leia. Everything else he does in the movies is strictly related to rescuing people and blowing things up. Unless he explicitly states he is strictly heterosexual, there are other possibilities.
Once again, any character that happens to be anything other than heterosexual is "just there to make a statement". It only feels this way because we live in a hetero-normative world where that is the default. There are plenty of characters in movies where a character just happens to be defined as heterosexual, despite not doing anything romantic in the film. I doubt you complain about that,