It's generally not, because you can run an OS on a PS5 that can then run the game, and the DMCA allows for this (with some limitations) because, and this is a very important point: there is generally no DRM-hacking required. But...if DRM hacking is required to get a PC game to work on a PS5, it's illegal to do so under the DMCA. (Note: DRM is defined very broadly for DMCA purposes.)

Dolphin does require a bit of DRM hacking, but Dolphin (arguably) falls under one of the DCMA exceptions for archival use purposes. This is the second important point: the Dolphin emulates a system which has not been on sale for a decade. It's still possible* to use it for general piracy instead of archival access, but the archival use trumps the piracy concern. (It would be different though if the Dolphin developers started offering Dolphin on a commercial basis.)

But Yuzu is a commercial offering, for a console that is still on sale, and its use requires DRM hacking. So it's got 3 fatal flaws.

The only surprise is that Nintendo let it live as long as it has. You can bet they won't make that mistake again with their next console.