Letters and text are both written word. I see absolutely no difference in nuance and subtlety.
However, In most cases a letter leaves the sender and they don’t see it again assuming it’s a written one versus an email. A text stays with you until you delete it.
Unless you are an aunt of mine who photocopied a letter she sent berating a cousin of mine for how an event of hers happened. She then proceeded to show the letter to everybody on our side of the country.
Lack of public toilets in towns.