What about it? It’s a petal-shaped ultrawide hood. The hood for the RF 15-35 is similarly shallow. Look at hoods for EF ultrawides, they’re shallow, too. The long petals of the built-in hood on my 11-24 extend just 5 mm past the front element.
I’m pretty sure Canon can correctly determine the appropriate size and shape for a lens hood. Further, I’d hazard a guess they know more about optical design than you or me.
Again, what about it? Yes, the lens will probably have significant vignetting. Many RF lenses do. It’s readily correctable in the resulting images (yes, there’s the consequence of increased peripheral noise). Consider the awful distortion and substantial vignetting of the 14-35/4L, bad enough that Canon forces the corrections for in-camera JPGs and in RAW conversions with DPP (i.e., unlike other lenses those corrections cannot be turned off). They do that on a $1600 L-series lens, why would it be a surprise on a $300 non-L lens? However, we actually don’t know anything about the optical performance of the 16/2.8 yet.
As I said, it’s a FF lens. Period.