DNGs have added benefits, like including compression (optional) (either lossy or lossless) and error correction bytes to prevent corruption (optional). Even if there's some concerns like unique features or performance, I'd still rather use DNGs without these features and with reduced performance.
I always archive my RAWs as lossy compressed DNGs with error correction and without thumbnails to save space and some added "safety".
GFX 100s II’s apply a transform to RAW data at iso 80, see: https://blog.kasson.com/gfx-100-ii/the-reason-for-the-gfz-10...
I don’t know much about ARW, but I do know that they offer a lossy compressed format - so it’s not just straight off the sensor integer values in that case either.
Typically you want to pack them to avoid storing 30% of zeros. So often the bytes need unscrambling.
Any sometimes there is a dark offset: In a really dark area of an image, random noise around zero can also go negative a little. You don't want to clip that off, and you don't want to use signed integers. So there typically is a small offset.
The GFX 100s II thing is very interesting. Totally not what I would expect from such a "high end" camera.