Then why have Sanji use it at all vs Pageone?
He was setting up Sanji's end of arc fight - Pageone.
Nothing else makes sense with the information we have so far.
Choose one or more points as you please:
1) Sanji wanted to get rid of him as fast as possible since he was wrecking the city and its people and more Beast Pirates were expected any moment now.
2) He wanted to try the Raid Suit in an actual fight as a test.
3) Oda wanted to show us how Germa's Black Stealth looks because Usopp and Franky are expected to modify it and odds are they will remodel its looks, not only its abilities, for them to fit Sanji better.
4) A deeper conflict with Queen is set up through Page One's defeat (who in my opinion was clearly defeated with that last kick from the highs, and wouldn't make much sense for Sanji to not keep his words; things weren't looking good for Page One either, the amount of damage was unbalanced, was lost with Sanji's invisibility and was overconfident on his abilities).
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arent numbers like even below headliners?
I'd say the Numbers aren't Beast Pirates so they aren't above nor below any of their ranks.