Graphene is actually considered the hardest for the fact that in its monolithic form, it still has that much strength in it, unlike diamond and Wurtzite Boron Nitride which are blocks of materials. I think Wurtzite Boron Nitride only has better indent strength than diamond, I don't think it is harder.
Thanks for the kind words. I appreciate you coming around
Alright bro. I think i will make more research on what you've said. I will let you know what i come up with making the research. Thanks for the break down