They had to violate it to be able to sue. That's not malicious.

That’s simply a false statement, and it’s hard for me to believe you don’t know that, since it’s easily checked.

How would they have standing to bring a suit if they had not tried to challenge the Appstore rule?

Anyone can sue over unlawful contract terms without needing to breach the contract.

The one finding in Epic’s favor was that Apple violated California’s Unfair Competition law by preventing Epic from linking to an outside payment method.

Epic could have sued over that at any time.