No, it is not equivalent. A full build in a cartridge is playable beginning to end. It may be missing bug fixes, tuning changes or expansions, but it is a full game.

The Switch in particular has games that look physical but aren't, and nobody should consider those physical releases, but physical games that actually are physical games aren't equivalent to digital releases just because there is additional content that is digital-only. You lose me there, that premise is just incorrect. And even if it wasn't, preserving the 1.0 vanilla version of a game is as relevant as preserving the all-bells-and-whistles last patch with all DLC. Ultimately for full archival purposes both are relevant, so I'd rather have one of those frozen in carbonite than neither.

Now, I agree that DRM-free releases are a better way to handle this than DRMd releases, and I do agree that jailbreaking and backing up digital copies of DRMd releases is crucial for preservation.

But that is neither here nor there. For practical usage, as a sustainable artefact and as a preservable snapshot of a media release a physical version is absolutely crucial.