It is pre-emptive since the danger of Chinese apps is still hypothetical (and cyber attacks are way more relevant to national security than consumer apps anyway).
Consider it economic protectionism; not national security. China will not let western companies succeed and compete fairly. Thus, companies with access to both Chinese and USA markets (ie those from China) have a huge advantage.
Not true. You heard of Tesla? Its doing quite well and has majority stake. Things have gotten lot better but it been buried under the propaganda
So Facebook and google are unblocked now? Reddit? Quora? The internet situation isn’t getting better, if anything it is getting worse: China keeps improving their anti-VPN tech and the GFW is bound to include Hong Kong in the near future.