Another thing to remember about Cyborg is that Johns is the age where his first exposure to Cyborg may have been his appearance on the Superfriends cartoon, where he was already viewed as being a (albeit new) contemporary of that cast. So it's possible that making Cyborg a founder just felt "right" because he was originally seen standing side-by-side with Superman, Batman, etc.

Personally, I'd be good with saying the original 7 members were the actual original 7 (Trinity, Hal, Barry, Arthur, and J'onn) and then just letting that go, rather than using it as a crutch that any other incarnation of the league has to be set around. But if they had to tweak history and bring in a new founder, I agree with Black Lightning (love Vixen, but also like her coming in as part of the Detroit era). Yes, Isabella can be a pain, but DC has given him repeated opportunities to write the character "correctly" over the years, only to have bland stories that nobody cares about as the results. I'm sorry he feels that he got a raw deal, and maybe he did, but if he spent as much time focusing on writing as he does complaining about how others handle the character, maybe he'd be able to produce something that people actually want to read.