It is for now but it doesn't have to be. Dynamo's design isn't particularly amenable to dynamic and heterogenous shard topologies however.
There could exist a fantasy database where you still tell it your hash and range keys, which are roughly how you tell the database which data isn't closely related to each other and which data is (and which you may want to scan) but instead of hard provisioning shard capacity it automagically splits shards when they hotspot and doesn't rely consistent hashing so that every shard can be sized differently depending on how hot it is.
Right now such a database doesn't exist AFAICT as most places that need something the scales big enough also generally have the skill to avoid most of the pitfalls that cause problems on simple databases like Dynamo.
There could exist a fantasy database where you still tell it your hash and range keys, which are roughly how you tell the database which data isn't closely related to each other and which data is (and which you may want to scan) but instead of hard provisioning shard capacity it automagically splits shards when they hotspot and doesn't rely consistent hashing so that every shard can be sized differently depending on how hot it is.
Right now such a database doesn't exist AFAICT as most places that need something the scales big enough also generally have the skill to avoid most of the pitfalls that cause problems on simple databases like Dynamo.