How would you compare your product with https://www.blazegraph.com/, which has similar feature set, but is much longer on market, and has wider adaptation(e.g. powers wikidata)?
Grakn sits a layer above this in that is a knowledge graph. You can think of a knowledge graph as a property graph consolidated by an ontology or schema which enables it to encapsulate domain specific information in a structured manner. This in turn enables more advance features such as the automatic resolution of data based on pre defined rules.
You could indeed build a knowledge graph using Blazegraph (or any other property graph) but you would have to go through all the pains of coming up with an integrated and flexible schema as well as a resolution mechanism. Grakn comes with these things out of the box.
So Grakn is not competing with Blazegraph but rather builds on the core principals used by Blazegraph, TitanDB, JanusGraph, and other property graph systems. It builds on it to provide a structured yet flexible graph as well as a built in resolution system.