Black Adam doesn't have to be huge, a guy with a moderately muscular body would be fine it's not like he got his powers at the gym
I know people want them to look just like the comic book characters but that's not always realistic. I remember the first time I saw pictures of Ian McKellen as Magneto before the first X-Men movie came out I couldn't believe a frail looking old man was going to be playing that muscular old guy from the comics/cartoons but I think he won most people over with the way he played the character.
I'm sure there is someone out there of Middle Eastern descent who can fill out a suit just fine, I'm not one of those people who's totally hung up on "representation" especially when it's for people from a fake country but it just doesn't seem to me that a Black/Samoan guy with very limited range was the only or best option they had.