If you use multi-hop VPN then ISP only can see IP of the entry node and everything else can only see the exit node IP address. So your ISP doesn't know your exit node's IP address and your services doesn't know entry node's IP address. That gives you privacy from ISP and makes it difficult for ISP to link your activity in other services based on IP address.
If a lot of people use that exit node then you can blend in with others to have more privacy even if you're connected to Google account. Creating a anonymous/pseudonymous Google account over a VPN can take your privacy even further.