I know. That's my original point. Nami's weapon just got even more unique, whilst Yamao's is as barebones generic as they come.
I know she's a staff user. But she just got a power up that now lets her use a club. If Oda was going to have a character join the crew whose main fighting style involved swinging a club around, then why would he give an existing member a brand new ability that lets them do exactly that, but in a far more creative, unique and special way?
Someone new is going to join the crew that fights with a club...So let's give an existing member an upgrade that ALSO lets her fight with a club! But not only that... Let's make this a talking club. Heck, a talking club that can attack on its own!
How does that make any sense? Nami's weapon outshines Yamao's in every possible way. And it was so unnecessary of an upgrade. You'd think Oda would make Yamao's powers more unique, not less.