Giant Robot can't free Bonney, it makes narratively 0 sense. You don't understand the narrative if you think that, sorry. It's just some powerscaling nonsense from people who think that Luffy can't go back to Gear 5 and save Bonney.
- Bonney asked if Nika would liberate her at the beginning of the flashback.
- Bonney used an attack "give me a Nika-like future"
- Bonney saw Luffy's poster but she didn't realize that this was Nika
This is all heading towards Nika freeing Bonney from Saturn and Bonney realizing that Luffy is Nika, it's the perfect moment to do it.
When Luffy frees Bonney from Saturn, the ancient robot may AT THAT MOMENT move but it relies on the drums of liberation to work in the first place so the ancient robot can only awaken while Luffy is in Gear 5.