There wasn't any real demand for such political rights in Hong Kong, because that would have meant independence and not autonomy. You're welcome to show me one of the main pro-democracy parties making it a part of their manifesto pre-2012 to seek powers on those areas, but I can't recall it.
Plus Beijing has repeatedly "interpreted" the law to its own advantage, and the very fact it has now imposed this law on Hong Kong goes to show it could have directly intervened if a Chief Executive had overstepped their authority.
There was never a threat of Hong Kong taking defence or foreign policy powers, either legally or de facto.
I don't think that's the case at all. Up until the shitty "reform" package, relations between HK and mainland China were fine. Then it came out that the CCP wanted to remove any choice from the election by limiting the field to 2 or 3 candidates its allies in HK would pick. But it didn't stop there. There was the kidnapping of the Causeway Bay Books staff, the unnecessary order that mainland Chinese security personnel could be staffed inside Hong Kong at the railway station, the extradition treaty, the police brutality following the protests, the fact that Beijing was perceived to order Lam to stay in office rather than resign, the veto on an independent investigation into the policing of the protests, etc. You can say that the CCP wasn't behind everything, but when its directly interfering on some of those things it can't then pretend it has no influence on the rest.
Individually these things might not have caused a problem, but together it's completely understandable why a lot of HKers started being openly hostile towards the CCP over the years.
That sounds an awful lot like victim blaming. "Everything in Hong Kong would have been fine if locals had just kept quiet and accepted the political scraps thrown from Beijing's table."