She wasn't faking it though. She really had the power to rule the world. It's just that she was born in a time where some other reincarnators were already stronger than her. As Yuuki said, if she had been born 10 years earlier she could have ruled the world.
Thats true but she was also wayyyyy too confident and full of herself. It felt like she was going to be this big thing but it was so underwhelming lmao
I totally get that. She felt like she'd be more of a big deal yea. Especially because of her arrogance and how she was introduced. But in the end she was just another "I think my powers are unbeatable, so I've become very arrogant and think I can rule over everyone" type of villains we've seen in tons of different manga...
Maribel is straight up "fake it till you make it" except she never made it LOLLLL