The other feature is deniability: having an encrypted message and it’s decryption doesn’t give you any more information than a screenshot of the message in signal. There isn’t a way for the encrypted message to prove that it was legitimate as the previous keys are revealed in a way that means anyone sniffing the traffic could make a message encrypted with that key.
Of course, email goes between servers and then you definitely want to ensure the encryption is solid (it often isn't, so PGP is definitely good). I'm just saying that Wire/Signal/Threema/etc. having better encryption is in my opinion only important when you use Wire's/Signal's/Threema's servers. If you can and do host your own, especially if you host it at home, then in practice there is no difference.
Since most people don't do that, Signal/Wire/Threema/Matrix are of course the better options than PGP+email, but PGP+email is still an improvement over the status quo.
