For the parent: and not only bottlenecked at single hops but also hampered by the propagation of latency as the hops increase, depending on the complexity of the distributed system design.

> […] by the propagation of latency as the hops increase […]

Which is why you get network topologies other than 'just' fat tree in HPC networks:

* https://www.hpcwire.com/2019/07/15/super-connecting-the-supe...

* https://en.wikipedia.org/wiki/Torus_interconnect

HPC?

HPC = High-Performance Computing

https://en.wikipedia.org/wiki/High-performance_computing