The parent post is suggesting that 5 Million customers does not in any way imply 200 shards. It's much more likely that with 5M customers you have 1 or 2 shards

The parent post is suggesting that 5 Million customers does not in any way imply 200 shards. It's much more likely that with 5M customers you have 1 or 2 shards. That's 4KB (one document) per customer.