Well, I can tell you one: Opencart Extension Store. If you make a module, or plugin or extension and sell it there, they only charges 20% and they pay you using paypal. 
So, for 70% only of my work, minus taxes and minus bank transfer(They should use paypal to send us our money instead) taxes, I consider too little. And they can even use our stuff to marketing without paying us. Can we use Epic brands the same way?
And, generally, when we sell something like these kind of stuff here, it has a license for one product only. People buy a model, and it can use only for one game. If they want to use it on another game, they should pay another license again. But no, Epic wants us to license it for life and for any amount of products people do. Do we pay Epic royalties for just only one game and that is it, if we ever release it, or do we have to pay for each game that we make with the engine?
I was going to release the ledge climbing system that I am doing for free here, but my wife got fired, and that made change my mind, because bills are coming in like crazy. So, I decide to sell it for a small price on Marketplace. But in order to really be worth, with kind of rules and revenue split, it would have to be too expensive. 
And we still have : “All assets must be fully functional with the latest Unreal Engine.”
So, if still have be paying Epic for the subscription.