I think it's reasonable to argue that the opium wars did contribute to the demise of the Qing dynasty and spur the generation that eventually overthrew the dynasty. But even if we assume the colonisation of HK did not happen, the civil war between KMT and CPC wouldn't have differed much from what actually happened. Based on that assumption, the chaotic decades of the early PRC would likely be the same even without HK being a British colony. Now considering China in the 70s & 80s didn't have a domestic entertainment and music industry that can rival HK, it would be logical to conclude the same would still be case had HK never been colonised.
As for HK being crucial to the opening up and modernisation of China, again the institutions and connections HK had with the West were important and fast tracked the development of China in no small part IMO. Of course China could have done that without HK for sure, but why was Shenzhen chosen as the first Special Economic Zone, its proximity to HK was the reason.
Don't get me wrong, I'm not saying the above justify the unfair treaties and colonisation of HK at all. But the colonised HK did serve two useful purposes, or one if you dismiss Cantopop. Also the British did profit tremendously from that no doubt as they didn't do it out of charity.