Well, there are other ways to compete.
Epic could try to differentiate it self from steam by offering new and or better services on the platform.
They could also take a cut similar or closer to Valve's 30% and pass the 'savings' onto the consumer by lowering prices.
They could try to offer better support/customer service - does Epic even have an answer to the refund system on Steam?
They could develop great games in house and make them exclusive to the platform.
I dont buy it.