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.