Unity doesn't get a "cut" of your game profits, anyway. They get $1500/year/developer.
So, by eliminating the 5% engine royalty for its own store, Epic is making Unreal also free and thus engine choice is not a deciding factor in whether to use Epic's store.
IOW/tldr: Unity and Unreal cost the same amount of money to use and license if you sell through the Epic store.
Just fyi: that is not how the unity license works. Unity's license is if your company makes >= $100k a year you're required to buy the $400 per seat license. If your company makes >= $200k year you're required to by the $1500 per seat license. Period. So for example if you're employee of Google and in your 20% time you download Unity you are not allowed to use it for free. Google makes X billion a year. That's greater than $200k a year. All employees of Google who download Unity for work related purposes are required to have the $1500 per year seat license.
This has nothing to do with whether or not you publish a game. Unity is sold similar to Photoshop. It's a subscription. The only difference is unlike Photoshop, Unity has a free tier for people and companies that make less than $100k a year.
From the unity site
Free version eligibility: I or my company generate annual revenues or raised funds less than $100k
Plus version eligibility: I or my company generate annual revenue or funds raised of $200k or less
Other than that, you've just restated what I already said. Unity provides the tools on subscription, but does not charge a royalty anymore.
Epic is certainly not making the store engine neutral. It costs less to use unreal than unity.