Ofcourse he is doing it for himself..why wouldn't he?He believes his character needs the movie for fleshing the character out and introducing it to audiences.He wants the movie to be best and his character to be liked/entertaining for the audience.He pushed for it.He got it done because clout.Just like batman had clout even after bvs and jl.
And Nobody can say black adam is meant to be some weakling.The character from inception is captain marvel's anti-thetical equal.Cap,superman,ww..etc were all created to be top dogs respectively of the world they occupied..Before they were shoved together into one shared universe.
As for being the top dog,some character has to be.I prefer black adam over batman.did robert Downey do ironman for ironman?Ironman was the center of mcu.