AWS account ID == Your IP address. It may be sensitive, but someone needs to know it to get s*$t done. Illustrative example: I had to deal with a third party that we needed to integrate with because of anti-money laundering procedures a year or two ago. I wanted my team to setup a privatelink with the organization because that's generally more secure than an open sftp port. The company refused citing security reasons…
AWS PrivateLink has another property that generally makes it undesirable for these types of integrations: communication is bidirectional, and IP subnets should not overlap. We (as a vendor ourselves) typically integrate as a VPC Endpoint Service, where communication is unidirectional and our service is exposed as a load balancer’s endpoint within the customer’s VPC.
VPC endpoints seem preferable in this situation.