Okay, they're friends, as I said.
Thats not a recruitment drive LMFAO
That's them saying GOODBYE for fuck sake
Vivi isnt' a Strawhat until she asks to join the crew, or accepts an invitation to join the crew. Until then, she's just an ally.
Is Coby a Strawhat? Is Rebecca? Is Shirahoshi? I mean, we have this panel for her:
What makes Vivi special other than the fact she was the first long term ally they ever acquired?
In fact, is there anything that makes Vivi any more important than the SHGF? Nah. There isn't. I get it, you fucking love the character and that's great, but love her for what she is, not what you wish for her to be. These are mutually exclusive.