Other products include Macs and PCs, which allow "sideloading" by default, out of the box. Why are game consoles the relevant comparison? There's nothing in US law that says smartphones are supposed to be treated the same as game consoles.
iPhone was not originally a game console. (Apple itself almost never makes games.) Indeed, iPhone was not originally a store either. Apple argued in court that App Store is not a separate product from iPhone, but that's easily historically refuted: iPhone shipped in 2007 without App Store! App Store was added a year later, so it's obviously not essential to the product. And IAP aren't essential to App Store either, because they weren't added until 2009.
It was developers like Epic who showed iPhone could be a gaming platform. Apple itself has a pretty poor history at gaming, and the Mac has always been subpar compared to Windows.