Oda said 3 most important SHs are Luffy, Zoro and Nami lirc. So don't sleep on them.
It's obvious Luffy is captain so most relevant but tbh, all SHs are relevant in their own way.
Zoro relevancy is clear when Nami said if they wanted to pick fight with BM they would have brought Zoro along (Remember we had both Luffy and sanji there)
Nami is navigator - her skills helped SHs sailed to the present
Sanji is cook - keeps SHs healthy
Robin will play crucial role in reading Rio
And so on...
All SHs matters equally. Saying this or that is more relevant is just so shallow perspective.