If core developers are bought up by a single company, I'd be wary of the future control, direction and progress of the project. The open source version would likely stagnate as the commercial version gains features. It'd be hard not to align with company goals and plans when your paycheck depends on it.
Better would be to use mechanisms that already exist to sponsor the core developers for a length of time (Patreon, liberapay, etc). Alternatively, companies like Amazon could create an internal fund that assists key open source projects they've commercialized to set up as non-profits and then makes donations to them over X number of years.
I agree, there is a certain potential danger associated with it, however, it seems like there are quite a few cases where it worked out great.
A specific example that comes to mind, one of the main core developers of Webpack (Sean) got hired by Microsoft to essentially just work on Webpack on MSFT paycheck (I think now he branched out a tiny bit into other adjacent areas as well, but he is still one of the main Webpack contributors). I think it worked out great partially because he was not the sole creator, but just one of the few, and he was the only one who went to MSFT, so the other core devs still had some level of control they could exercise on their own without anyone being able to tell them otherwise.
There are definitely cases where it seems to have worked out. My sense, like yours, is that it largely depends on how "community driven" the project is at that point. If it has many independent core developers/main contributors, or many diverse companies relying on it, it seems to work ok (for now).
That said, it feels like there is a missed opportunity in the space. Most large companies already donate money toward interests in their local communities, etc. Why isn't there an easy mechanism for tech companies to donate to sustainable funding of open-source that they all depend on? My guess is that because open-source projects are rarely set up as organizations, they can't achieve 501(c)(3). It would not only be tax advantageous for companies, but would also support business continuity and recruiting pipelines. It would also be great for open-source developers and the community.
Maybe there are efforts out there to create something like this?
Better would be to use mechanisms that already exist to sponsor the core developers for a length of time (Patreon, liberapay, etc). Alternatively, companies like Amazon could create an internal fund that assists key open source projects they've commercialized to set up as non-profits and then makes donations to them over X number of years.