I've done this exact upgrade on 17 Nutanix nodes (ESXi 6.7 to ESXi 7.0) however I used the Nutanix 'Prism Element' GUI, not the CLI of the hypervisor to do it.
Log into Prism Element, go to 'settings', 'upgrade software', select hypervisor, upload the 7.0 hypervisor iso (after you check compatibility for your hardware: https://portal.nutanix.com/page/documents/compatibility-interoperability-matrix) then press update!
Prism will update one node at a time, and not start updating the next node until data resiliency at your chosen replication factor on your cluster has returned again (ie after a node is updated successful and enough time has passed for metadata to be shared again on the node that has been off for a little while).
Afterwards in vSphere center, check compliance of the nodes on the Updates tab & remediate any patches needed since the ISO you used was released.
Hope this helps!
VCP-DVC 2022 & CCNA