Neo4j is by far used more than any other graph database out there. Regardless, the standard is not Neo4j specific. It was a collaboration from many companies in the space. They all agree it's a good move.
I think even Cosmos as number 2 might be misleading here, as Cosmos is a multi-model product and db engines doesn't distinguish between graph and non-graph use in the ranking. (Same for ArangoDB)
As a contrast, the recently introduced RedisGraph only supports Cypher.