Did you finish reading the wikipedia page you linked?

In contrast to the hammer,

In contrast, non-rival goods may be consumed by one consumer without preventing simultaneous consumption by others

Can you and I both use the API at the same time? YES!

There's also this:

For instance, use of public roads, the Internet, or police/law courts is non-rival up to a certain capacity, after which congestion means that each additional user decreases speed for others. For that, recent economic theory views rivalry as a continuum, not as a binary category,[4] where many goods are somewhere between the two extremes of completely rival and completely non-rival. A perfectly non-rival good can be consumed simultaneously by an unlimited number of consumers.

Your argument against roads applies directly as a metaphor to IP banning. Its the same principle.
Funny enough, one could make the argument that more usage of an API node increases efficiency of the access -- this is due to locality and caching behaviour. When two people access the same resource, the server only has to prepare that resource once before delivering it twice -- making it faster access for the second user. This is an anti-rivalrous property. :)

It is very practical to restrict access to servers with API keys.

It's also possible to blow up a road. This doesn't mean a road isn't a quasi-public good anymore, it means you changed the underlying properties and thus changed the good. If you don't use API keys on a server, its not restricting access. Sure, I could change it to be a private good, but I'm not.

I'm willing to meet you half way here, but I'm surprised you're unwilling to move an inch. It's quite clear to me that this falls quite high on the spectrum of "public goodness" while being obviously not a puritan perfect one. But very few things are puritan perfect ones -- even a beautiful scenic view is worth shit if overcrowded or polluted. I don't think that you thinking in absolutes is a good way to approach this.