The benefit of partial ownership (or dual ownership) is that it opens up the network of internal employees and management to recruitment while also providing plausible cover as it is a branded and well-known "western" firm
That's one or two other shareholders you need to bribe / convince. Not difficult, especially when the company you just invested in is learning what it's like to have scrooge McDuck money and want more.
This depends a lot on who owns the other 60%. If it's one other party, the 40% effectively has no control. If it's a public company with a million other owners and they're the largest individual shareholder, many of the others won't even show up to vote their shares and their 40% of all shares will generally be >50% of the ones that show up to vote for anything.
A more reasonable case is that they can heavily influence what contractors and 3rd parties are used for projects. Not something that needs a board vote, but something a 40% shareholder has a lot of say in.
The literal thing I just said isn't even that unethical; suppose you own 100% of a company, then telling it to hire someone specific and pay them this much and put them here would be fully within your rights as owner. (There's probably a legal hurdle or two to clear, but AFAIK it's nothing that will actually stop you.) How that changes ethically as your ownership stake decreases I'll leave as an exercise for the reader. What's unethical is what they'll be doing when they get there, and who else is tainted ethically depends on how much they know and what they do about it.
But you would get to heavily influence what contractors and vendors the company works with are good vectors.
As well as partnership and integrations.
Heck, if China wants to spy on anybody, they don't even need to resort to technology to begin with... Unlike the PRC, USA is a more or less open society — want someone's secret? Just send your man there; Want to influence someone? Just ask......
I totally don't understand American concern with technology being used by espionage, while it lets this go.
Yes, stealing individual secrets is best done with old school tradecraft. Spies in suits, photos of scandals with dominatrixes.
But what if you want build a system which can identify homosexuals based on textual conversations? You buy Grindr.
Or what if you want to get a backdoor for future exploitation on almost every computer in the US? You buy Fortnite. Because one of those computers will belong to the child of someone important. It only takes one slip by them to get Stuxnet from their home PC to their work PC.
You mustn't be afraid to dream a little bigger darling.
I shouldn't have mentioned attack vectors, the first case is the better opportunity these days. Data data data.
Why would anybody need to do more than steal individual secrets they've been told to recon?
You can build that model if you have access to the data of 20 million people.
No comment on the wider claims, but 40% does give them a tremendous amount of at least soft power.