The marks will be due to shit going through the pump
And the poor presure is due to lazy tolerances whether there in the pump
Or in the engine ( shells )
You need to remember that a pump of any type is not the only factor in
Making presure , as there is far more opportunities for presure to be lost
In the engine than in the pump .

When buying one of these pumps it would not hurt to check the tolerances inside
Rather than assuming they are spot on
( but yes they should be )

As for the hex drive it prob does feel like a lot of movement
As a little feel a lot , but as for mm it would be spinning inside its self

You can feeler gauge the clearance to find out what it is
But some of that clearance is to get rid of any miss alinement between the pump/drive/dizzy