This seems to be the standard that all store fronts use. With maybe an exception on epic who purposefully went lower than the industry norm to try and excite game publishers to their storefront.
Just from some cursory googling - google and Apple are right in line. 30% with some drops into the 15% mark after time has passed in case of subscription payments.
Edit: have not been following this story but it seems like kind of an uphill battle. We know what the argument will be - it’s x percent but you’re using our product and infrastructure and we have to invest people and resources to verifying apps getting published.
Feels like the law suits that involve “allowing multiple app stores” had a higher chance of succeeding (though I have no idea the status of those lawsuits so maybe that’s already off the table)