The discussion on the SSC subreddit has some good pushback in the other direction that offers arguments against the vulnerabilities the OP is suggesting.
Short summary:
redundancy as a form of security is already industry standard
shared system vulnerabilities can also have benefits like common knowledge and solutions generalizing to the whole system.
actual scenarios discussed in OP would likely not be as bad, like the solar panel one
The discussion on the SSC subreddit has some good pushback in the other direction that offers arguments against the vulnerabilities the OP is suggesting.
Short summary:
redundancy as a form of security is already industry standard
shared system vulnerabilities can also have benefits like common knowledge and solutions generalizing to the whole system.
actual scenarios discussed in OP would likely not be as bad, like the solar panel one