Really nice and clear. One addition: the final example uses ProxyCommand, I find ProxyJump much more useful: you can specify multiple hops clearly and even specify different private keys for each hop.
ProxyCommand is useful for proxying with a non-SSH protocol. For example when combined with proxytunnel or similar you can run your SSH connections over an HTTPS proxy, which appears as regular web traffic to the network operator.
ProxyJump indeed seems more useful, but has less support (it's a "newer" SSH feature). Do you know if it needs to be supported by the openssh libs of intermediate hosts, or just the initiating client?
As far as I remember, it‘s implemented on the client only. (It can be replicated with ProxyCommand and a few invocations of cat/nc on the proxy host, if I remember correctly.)