I should have gone into more detail, but it's because of many of the things you mentioned. Flu vaccines are not "new" .. the procedure for making them is well known and many strains are made and kept ahead of them. (I believe they're all inactivated virus, typically bread in chicken eggs). They aren't made in six months; they took decades to develop the process where strains can be isolated, inactivated and combined in a shot.
SARS1 vaccines had some very troubling imunopathic responses and feline SARS1 vaccines made reinfections worse. This will be a totally new vaccine, for a virus family we've never developed vaccines for before, and some of the techniques they're using (the DNA/RNA technique pushed by Gavi/Gates) has never had a vaccine make it through a clinical trial before.
Those are the troubling things. I wrote more about it here:
https://battlepenguin.com/politics/this-is-not-a-time-of-hon...