Hmmmm, I've never given this any thought, it is a good point. It's strange that kuma would even have the knowledge to send each strawhat to where they could have gotten upgrades. Also, in general kuma sending people places is not exactly a good explanation as to how things developed.
Luffy: Kuja island.
Zoro: Kurugaina Island
Sanji:Okama Island
Franky: Some future island
Robin: That bridge thing
Brook: Namakura Island
Nami: Some sky Island
Ussop:Greenstone
Chopper: Torino Island
Some of this are easy, though not exactly in the powerup sense. Robin was sent to the revolutionaries, franky to a place he could improve his tech, nami to a place where she could learn about weather, chopper to a library. But then luffy in kuja islan... You'd think that's somewhat of a death sentence. Sanji at okama island? It seems almost like luck helped ivankov get back there and set up sanji's training. Kurugaina seems mostly empty, could kuma have planned anything that happened to zoro there? Greenstone? Was kuma's plan for ussop to meet heracles?
So... it's all pretty wonky. Perhaps looking at this from the place angle is not the answer. Perhaps kuma sent the strawhats towards people? But if he did, that also certainly does not explain a lot of strawhats. I suppose he could have pointed some strawhats towards people and others towards places. Though that requires super specific intel of each strawhat and perhaps even kuma deciding what was best for each which is even crazier. Not unviable but, um, damn. I wouldn't be surprised if it turns out this was simply luck an kuma has a sort of shuffle setting to his ability.