I also worked on a team that built something similar, and I've seen it done in other companies. With services like this, and others like Transit Gateway, it's getting a lot easier to manage multiple accounts and VPCs. I haven't tried AWS Control Tower yet, but I am hoping it gives easy visibility into all the accounts in one place. With Amazon accounts, once you assume a role into an account, you can't see other accounts without switching back into them.

This is one area where I think GCP got it right. By using organizations and projects within one account instead of having parent and child accounts, it's quite a bit easier to see what's going on. And a parent account has a very different role from child accounts, so it makes sense to treat them as separate things.