However: “Multi-document transactions are available for replica sets only. Transactions for sharded clusters are scheduled for MongoDB 4.2.” DynamoDB is sharded by design.
I see, it appears to come down to how each db interprets "partitions".
If we're referring specifically to shards then "DynamoDB is the only non-relational database that supports transactions across multiple partitions and tables." no longer sounds like hyperbole.
If we're referring specifically to shards then "DynamoDB is the only non-relational database that supports transactions across multiple partitions and tables." no longer sounds like hyperbole.