Well the point isn't necessarily that Black Adam is a complicated and deeply dramatic role, just that he does require a certain quality and range that not just any actor could bring. There are plenty of fantastic actors who have been miscast in roles that they just didn't have the right qualities for.
The Rock has shown himself to be very capable and charismatic in roles that exploit his talents...but he does have a limited range.
Still...I think he'll probably be ok in the part and I wouldn't be surprised if it was written/rewritten with him in mind just to make sure. I think he'll be ok as Adam.
My real issue is I think he could have been *GREAT* as Marvel.
For the origin story, BA is not going to have any other strong emotions besides anger and arrogance.
This isn't going to jump to DC's WWIII arc, or deal with his rule over Khandaq in current times, or the Black Marvel Family.
That said, he's matured enough as an actor to be able to handle a DC movie role.
They haven't had any characters that I would call "demanding" or "complex" outside of the Joker in the Batman Trilogy.
Everyone has been pretty simple.
In all honesty, for the origin story of Shazam and his first run in with Black Adam, he's going to be as dramatic as Zod, at most, which isn't very demanding.
