Depends how you define "adopted." In this case I personally was defining it as how many people are touching the code. You seemed to define it as how many systems rely on the code.
At the end of the day, we are all people using computers. We interact with code at all levels of the stack. In any given request cycle, a person is interacting with the hardware layer, application layer, operating system layer... and those of dozens of other external systems connected to the internet. Each layer, each system, is just as important as the others. Together they form the experience that is delivered to the user by the computer.
So I don't think you can place a value on the "importance" of a piece of software; all software should be created equal, so to speak. Therefore you cannot evaluate the "adoption" of a piece of software based on some multiple of its importance. You can only rely on the number of people that touch that software as an indicator of how many other people, or systems, might rely on it. If many people, and therefore systems, rely on a piece of software, then I would consider it "widely adopted."
Software has developers and consumers. Both are important.
React, Linux, BSD, Apache... they are all software projects. You cannot compare them based solely on what type of software they are. You need to look at the codependencies they create and the value they provide. Their value comes from the product that developers create, and consumers use. Their codependencies arrive when the consumers are also developers, who incorporate the code into their own project with its own consumer users.
Software with developer consumers is not necessarily more important than software with end user consumers. Neither can exist without the other.
So I guess I'm saying it was presumptuous of me to describe react with the superlative of "most widely adopted" software project (of all time), but I would put it in a class parallel to that of those projects you mentioned. Really, in one class -- software.