The closest thing I can think of wrt competitive rules is their price parity rule, where if you sell your steam keys (note that. not epic or uplay, just steam.) yourself, the price can't be noticeably lower (or a sale can't happen) without a comparable discount/sale on Steam within a reasonable timeframe.
That's pretty anti-competitive, unless I'm misunderstanding it.
If Epic takes a smaller cut, a developer might be willing to sell it at a lower price than on Steam. But if Steam says that the sale on Steam needs to be the same, then that means the developer can't put out the same sale on Steam (since Steam takes a bigger cut).
So instead, they'd have to make the sale price equal to the price they'd be willing to accept after taking Steam's cut into consideration...which would be higher than the price they'd be willing to sell for on Epic.
That's bad for developers AND consumers.