The value of an FID is in the social graph—both stated (following) and revealed (activity). Profile is secondary. There is minimal (no?) value in the onchain primitive absent the above.
This is why digital identity is always emergent from apps with utility. If you spend a lot of time using an app / platform / OS, it starts to become your identity. Building an identity layer is the wrong order of operations. You earn the right to be an identity layer by time spent, usage, people building on it, etc.
At-scale digital identities in 2024:
Email address — the original "killer app" of the internet; so naturally websites asked for you email address as your identity
Phone number — as smartphones became more popular, many apps shifted from asking for an email address to a phone number. Even more people had a phone number than an email address, esp. in developing countries.
OS-level identities — Sign in with Apple and Sign in with Google