Dominar means "to dominate" or "to control." It's a strong verb that goes beyond simple control, implying a forceful and often manipulative assertion of power.
In the context of Marília Mendonça's song, the singer confronts someone who is "acostumado a sempre dominar" (accustomed to always dominating). This word perfectly captures the antagonist's arrogant and controlling nature, setting the stage for the singer's defiance and refusal to be manipulated. It's a key word for understanding the power dynamics in the lyrics.
"Você Nem É Tudo Isso" is a sertanejo kiss-off aimed at a partner who thinks he's irresistible. The singer warns other people not to fall for his charm the way she once did, and tells him directly that he isn't as great as he believes.
She's watched him operate before, always in control, always working an angle, and she's no longer buying it. Where she used to get pulled in, she now stays quiet and pays attention, because she knows exactly how his game works.
The chorus is her line in the sand: he can play the same tricks on someone else, but not on her anymore.