I noticed this 1970s Hamilton has essentially a perfect circle between its 3 subdials. Not sure if this is part of the design or a circular scratch. Thoughts?

 

Might be caused by the hour hand. There are cases where the lume gets loose as circles around with the movement of the hand. Sometimes it can also be caused by rust or other particles

 

Anyone else also think it's a scratch rather than by design?

 

Here is what that dial should look like.

 

Yeah, it's hand drag. One of my watches has an identical mark.

 

If you service the watch, the watchmaker should be able to remove it. Doesn’t look like deep scratches

 

How would he do that? I didn’t realize such scratching can be easily removed.

 

If the dial has deep scratches the repair is going to be very hard but matching color can be added at the damaged spots.
But I think in your case there was just some material spread across the dial which can be removed with a brush or the Bergeron glue sticks.