Is AWS security boundary the AWS account? Are you expecting Vercel to provision and manage an AWS account per user? That doesn’t make any sense man, though makes sense if you’re a former AWS employee.

Yes the security boundary is the AWS account.

It doesn’t make sense for a random employee who mistakenly uses a third party app to compromise all of its users it’s a poor security architecture.

It’s about as insecure as having one Apache Server serving multiple customer’s accounts. No one who is concerned about security should ever use Vercel.