Did big businesses in the West really think “investing” in China would lead to “freedom” and such?

You’re right in your assumption that profit-seeking was the major part of it - like, it wouldn’t have happened otherwise.

But the idea that the West trading and interacting with China would mean the populous (and perhaps government) would come to understand the benefits of a free society, and so China would trend towards a Western political system - probably gradually rather than violently - was a mainstream view from the 80s to the early 2010s.