I’m afraid that’s not really correct. It seems like having less data on each shard will help, but think about linear scaling - if you double the number of shards, you want things to get twice as fast. And while the amount of data on each shard will be half what it was before, a scatter gather query will actually generate double the number of queries you had before.
The “magic” of sharding as a method for horizontal scaling lies in targeted queries, not scatter-gather queries.
Asya