Not so sure. After my father died I came across a box of old letters that were sent between he and his friends, from their early college years. Just personal, casual correspondence, which today would be done with a messaging app or email. Even on the short notes, the structure, spelling, grammar, and even the penmanship is excellent compared to what I see people of the same age doing today.

You had to dedicate so many more resources to that, though. Mailing a letter requires gathering up paper, a pen, an envelope, a stamp, and the person's address, then physically transporting it to a mailbox. It also has a lot of inherent latency, so you have to pack a lot of content into the message because it'll take as much effort into clarifying something you left out on the first message. It's natural to put more care into something you've invested that much baseline effort into.

I wouldn't spend nearly as much effort on something ephemeral and instant. For instance, I'm not going to mail my sister in another state a letter saying "ok thanks". I very while might text her that, because 1) she knows exactly what I'm referring to — the thing we were talking about 11 seconds earlier; 2) the customs of messaging mean she doesn't expect or want a wall of text; and 3) if she has any more questions, she can ask them and I'll reply within a minute or two.