They are an isolationist authoritarian nation, with already-large and still-growing influence over world politics and economic matters. Perhaps what the West is doing right now to attempt to curb this is the wrong move, but I don't think the "fear-mongering" is unwarranted at all.
Your first part doesn't really go with the second.
I agree, China is very isolationist. But that's precisely why I'm not concerned about this "influence". They're absolutely not interested in converting other countries to their system, they will work with anyone who they can do business with.
Foreign companies have a very large presence in China's internal market. It would be difficult to give a full overview, so I'll give a few examples to illustrate the point:
* Volkswagen has the largest share of the Chinese automobile market.
* China is Nvidia's 2nd largest market (nearly $4 billion in revenue, which is more than Nvidia takes in in the US or the EU).
* Airbus and Boeing dominate the aircraft market in China. Airbus just announced a $17 billion deal two days ago.
* Starbucks runs 6,000 locations in China.
There are countless examples like this. Suffice it to say that China is one of the most important markets for a very large fraction of multinationals.