I'd say that, but suppose it depends on where the writers take it.

I 'member me a golden age Shazam comic where he has to fight all six gods who give him powers, but he wins easily because he has their power, plus the powers of all the other gods. So he was literally more powerful than the whole pantheon.

Nope.

"Demigod" is not an indication of powerful, it's just heritage. Tons of people were demigods. Some of them, like Hermes, were even considered as full members of the pantheon. It's an awfully vague term.

Black Adam is just a man.

I've always seen "Demigod" as somebody who is part god, as in, either the mother or the father is a god/goddess but the other parent is a mortal so no, he's not

He's like a demigod, not a demigod.

It depends. You can be given the power of the gods and not become one or a demigod. If the powers you're granted specifically turn you into a demigod, then yes.

You're as powerful as the writers say you are. It's not rocket science.