I have Brook as the weakest imo. Still tho Stopping Hakuba is not the same as defeating him... Franky is seemingly growing thro fights and he can always get even stronger anytime he wants by modifying his body parts and weapons while Robin isnt showing interesting in anything related to combat...
It is. Hakuba is based on speed, Robin has the strength to twist Oars arm pre-TS, and she can create at least 10 times more arms post-TS, she twists Hakuba like a twig.
Franky has not done so though yet, he has the potential (i think Vegapunk arc will be a huge power up arc for him) but right now?
Robin > Franky > Brook.