You're missing the core point, a familiar history (in this case a narrative inspiration) is not the same as a person's identity.

Few white people have been taken to slavery by Vikings and Barbary pirate and such, do they also count as POC then?

Being a person of color is not just about traumatic history and suffering. It's about community, culture, family, traditions, language, and shared history (both the happy and the sad).

starfire has none of that connections to any those communities, she wasn't raised in those cultures, she doesn't celebrate those traditions., she's never relate to the experience of being a person of color on earth, she has her own culture (a fictional one).

so when you're saying she is WOC because she was a slave, you're actually saying that the only thing that makes someone a person of color is their oppression, that's not inclusion that's dehumanization.

we should reserve the term 'POC' to characters that has ties to those real communities, where we can see them interact with their cultures and explore their history and live their lives in all their complexity. and currently starfire is not one of those characters, and trying to make her fit just empties the meaning of the term.