It is easy enough--arguably easier, right?--to generate random keys, but if you always work with hashes of the key (which I am not claiming cockroach doesn't do, only that I would be frustrated if they do) then you lose the ability to do range queuries.

Cockroach lets you hash-shard your keys n-ways if you choose to through a feature called hash-sharded indexes (https://www.cockroachlabs.com/docs/stable/hash-sharded-index...) That's a trade-off: costlier range scans (a range scan turns into n scans) for avoiding a throughput-limiting hot spot.