"When it comes to Newsletter success, consistency, and by that I mean daily, is everything."
My favorite newsletter so far was Ruby Weekly, which I read every week for several years, and I can say I wouldn't have been interested in it for daily. So I disagree that "daily is everything".
Was? :-D Haha, but yes, I think your opinion is the most common one amongst readers. To be fair, Ruby has stablized/plateaued to such a point that even weekly is pushing it in terms of quality sometimes. There are ways to approach daily newsletters in quiet niches that can work, but it always helps if it's a fast moving space (so "tech news" is ideal for daily, say).
I don't use Ruby much anymore, and my regular inbox is cluttered. Just signed up for JavaScript, React, Node, and Golang weekly in my hey.com account :)
My favorite newsletter so far was Ruby Weekly, which I read every week for several years, and I can say I wouldn't have been interested in it for daily. So I disagree that "daily is everything".