I work at one such "medium sized" Google DCs. Supercomputers are typically much more interconnected, whilst we have a much more traditional topology.

Supercomputers are more about the network topology than raw processing power.

supercomputers, by tradition, are tightly coupled in a way that Google datacenter servers aren't. The closest thing Google has to supercomputers are GPUs linked by high performance networks, and TPUs (which have their own custom toroidal mesh).

Isn't the whole point of a supercomputer that it isn't just a datacentre with an LED display on the front?