That headline is half truth. Price of a cloud database depends on so many things. what is the I/O, what is the storage utilization, cross-region traffic, etc. Picking one scenario and claiming the cost to be half is too simplistic and a marketing gimmick.
Also which dynamo price are they comparing to? On demand? Provisioned? Reserved provisioned? We had a huge spanner db with low throughput so had to add idle nodes just for storage which also ballooned costs for spanner(the increased storage size here helps)
