> Phone numbers -> name resolution is done using your contact list. At least last time I checked.

Nope. With contacts permission granted, unknown numbers turn into ~names (per user's own profile) automatically. When you revoke the permission, the ~name is hidden to punish you.

> [...] there's no guarantee that my username reflects who I really am. Feels rightly more suspicious IMO to see a message from an unknown number than from "~Elon Musk".

It's an entirely separate problem, and as old as mail itself (which predates computers by many millenia). Would you know whether to trust [email protected], without looking it up?