Obviously they're different technologies, however the main purpose of their implementation is for reduced fees. There'd be no reason to implement these technologies otherwise
The main reason for Graphene is to allow for a more efficient block propagation. Nothing to do with fees.
Fascinating. I need to research this more and understand it more. Assuming it's true which seems likely, this needs to be much more widely dispersed information. Planck fee!
Maybe, in a unconstrained blockchain, like BCH is. Not in BTC. Miners in BCH could find that there is less risk of orphans with graphene, and could lower the min fees.