Right or wrong, copyright doesn't care about how valuable something is. Everything is equally (not in reality but in theory) protected. GitHub is a platform many people have trusted with protecting ownership of their copyrighted code through reasonable levels of security.
I think the big discussion point here is around ensuring that this tool is acting correctly and respecting rights of an individual. It's very easy for a large company to accidentally step on people and not realise it or brush it away. People want to make sure that isn't happening and right now there are some very compelling examples where it looks like this is happening. The fact that this isn't opt-in and there's no way to opt-out your public repositories means the choice has been taken away from people. Previously you were free to license your code as you see fit, now we have some examples of where that license may not be being respected as a result of an expensive GitHub feature.
I think this is where the conversation is centring. It's not about whether your code is valuable or not. It's whether a large company is making profit by stepping on an individuals right of ownership or not.
On the note of leveraging legal apparatus to figure it out I think you're right. The problem is what individual open source maintainer is going to have the funds to bring a reasonable equal legal challenge to such a large organisation? I maintain a relatively well used open source project and I sure as hell don't. Realistically my option is to either spend a lot of personal time and resources to challenge it (if I think wrong-doing is happening) or just suck it up. Given that there's no easy way to figure out if wrong-doing is happening because it's all in the AI soup, it makes it even harder to consider that approach.
I think the point is a lot less about the value of the code, and much more about a massively organisation playing hard and fast with an individuals rights.
None of this is to say GitHub have actually done anything wrong here. I'm sure we'll figure that out in time, but it would be great if they could figure out a way to provide more concrete explanations.