There is very little to taken away from the scrimmage. Much was played with a 7 on 11 format with no offensive linemen and no pass rushing. If anything, I think the QBs may have taken too long to get rid of the ball but that will come with real experience.
As for RB, I’ve just reviewed the tape of both DB and MB. They have very different running styles. They will both have their opportunities. Much of their success will be based on the effectiveness of the OL. MB may have more success running between the tackles but only time will tell. DB is faster, perhaps a lot faster. I would suspect he has the ability to get outside and turn in big runs. Someone compared his style to Erik Marsh. IMHO, if there is one position where players can transition up the easiest, it’s RB. They both may need to learn how to block though. That could be critical.