It's not splited or splited enough. Sadly this is the worst of the both worlds. Splited RAM, as we know from PCs would be preferable to this. But technically you just have the chips connected with less wires and since the topology of the memory is star not ring you don't get slowdowns to the slowest speeds (granted, if you are okay with 10GB for GPU data and 6GB for CPU, if you combine it, then yeah...). However you still have to deal with scheduling everything, because that command (how is it called, shit) processor is one, cause it had unified memory controller. So you are still dealing with limited number of data streams, which you can send it to the memory. Which frankly sucks, they should have did 6GB of DRR4 and 10 GB of GDDR6, but then the console would cost 700USD or more...
So no AF16x and all that shit, because you can't even spawn copies of the same thing in memory (you need feedback for texture, based on where it is, so you can calculate how to make it sharp), without causing to stall the spawn of new data streams for other things.
Edit: Worst of both worlds is probably not acurate, because I forgot about DDR3 + 32MB cache... Which, yeah that's a thing. STILL.