Not sure what you mean about Ceph wanting to be in a single rack.

I run Ceph at work. We have some clusters spanning 20 racks in a network fabric that has over 100 racks.

In a typical Leaf-Spine network architecture, you can easily have sub 100 microsecond network latency which would translate to sub millisecond Ceph latencies.

We have one site that is Leaf-Spine-SuperSpine, and the difference in network latency is barely measurable between machines in the same network pod and between different network pods.