Forwarding is a redirect, not an address
Email Routing takes a message sent to you@yourdomain.com and drops it into an inbox you already own. Nothing is stored on Cloudflare’s side. There is no account to log into, no folder structure, no archive — the mail lands wherever you pointed it, and that inbox is the real one.
For a lot of people that is exactly right. One person, one domain, a handful of aliases for shops and newsletters, all landing in a personal Gmail. Free, five minutes, done. We would rather tell you that than sell you a mailbox you do not need.
It stops being right the moment there is a second person. There is nobody to forward to, because your co-founder does not have an inbox on your domain — they have your forwarding rule, or nothing.