Joe Casey was never promised an America solo, I don't know where you guys are getting that from. He's been pissed at Marvel ever since Gillen's run of Young Avengers, and that was in 2013, he's been out of Marvel since then. He intended to make his own All-America series at Image back in 2016, and that's when Marvel came up with the America solo by Gabby Rivera, released in 2017.
And this new series (or should I say, one-shot, because that's all it is) was delayed once again when Marvel decided to make a new America miniseries this year, which still hasn't come out and will be released digitally. He's just mad because they "made" her a lesbian, even though there were hints of it in the Justice series. Say all you want about the America solo (and deservedly so), but he's acting as if he's the first creator whose creation has been handled by other people.