You could certainly get proofs from ION, as it contains all the data for them, but just hasn't been implemented yet. The issue with literally any construction, even L1 blockchain ones, is that you really must run some sort of light node to avoid Tip - N state issues.
Running an ION light node (a configuration that's provided for in the system, but has yet to be coded to provide) reduces the resource requirement by ~95%, making it feasible for users to run on most devices.
To own or take someone's ID string, you'd literally need to take control of their current recovery private keys, you can't Sybil your way to that.
Part of your confusion seems to stem from the idea that IDs are something you can register like an ENS/DNS name, wherein different people could end up with a string attributed to them. ION specifically removes this whole class of issues due to its self-certifying inception event for creation of IDs, and it's non-transferability properties.
That's not how creation and ownership of ION IDs worlds. You cannot attempt to create/own the same ID as another person, because the ID itself is entirely generated by the initial state of the IDs PKI (including the keys). This cryptographically secure, unique, immutable means of creating identifiers is know as a 'self-certifying inception event'.
Because all data related to DIDs in ION is DID-relative, and you cannot Sybil/own another person's IDs, your routing and data URLs are not susceptible to the type of issue you are describing.