They should sign an ethereum address to reduce ambiguity
(Any crypto asset address is fine, even PGP is good enough for this but PGP had 25 years to make that user friendly and common but failed, and cryptocurrencies made signing software more prevalent and uniform wayyyyy faster)
However, there's still some very good programs with good UX making use of PGP (for example delta.chat), and to this day no cryptomoney scam wallet has ever been as useful as PGP has over the years.
It really isn't. It uses CFB and does not have a MAC, while the format is overly complicated for no reason.