To the best of my knowledge the scaling behind distributed ranged KV stores (which cockroachDB uses as its storage engine) is easier to manage overall. Whether that's important for "serverless" is another question.

I'm sure PlanetScale will help with rebalancing and re-sharding but, just like FoundationDB, CockroachDB "promises" to automatically re-shard hot keys and ranges for you under the hood, and so _in theory_ scales well for a distributed read/write heavy system over many nodes with potential hotspots. My CockroachDB knowledge is based off of research into FoundationDB, but I think it shares many of the same underpinnings (even the record layer concept). And FoundationDB scales very well.

Vitess, on the other hand, manages the cluster for you but I don't think that the rebalancing and sharding is as easy to manage. Would love to learn more as I don't know much about Vitess.