It's only pre-season, and they played with a different makeshift back 4 in each half, so I wouldn't take a great deal from getting beat 4-2 by AC today.
I want them to fail this season as much as everyone else but I don't think today's result is really a marker for anything significant.
It tells us than vanDick isn't able to do the work of 2 centre-backs, and outside of their starting back 4 they haven't got that much quality. We knew both of those things already, but we also know that their inhaler addiction sees them field a fairly regular back 4 most weeks.
Injuries to any of the 4 will be key to their success/failure I reckon.