Personally, I find this overly simplistic and I believe it's misleading. I write, review, and edit professionally as about 1/2 of my current job, and I see tons of awful writing by people who write every week. Believing you just need to write regularly to improve is like believing that if you play tons of gigs on your instrument you'll get better. How many really bad musicians have you seen who have been stuck at basically the same level for many years, but play all the time? So, so many. It's just not true.

To really improve, in addition to writing you need to:

- Read really good writing. A lot. Every good writer I've met is a voracious reader and has been for a long time.

- Read about writing, as in, actually study writing

- Edit and review your writing, and get your writing reviewed and critiqued by people actually qualified to comment on quality writing

If you aren't doing this, a daily habit might get a lot written, but it could stay crappy for your whole life. I would argue that real study and less production writing is actually a better use of your time.

Some of my favourite books to start on serious study:

"A Sense of Style" - Steven Pinker

"The Making of A Story" Alice LaPlante

"Steering the Craft" - Ursula Le Guin

"On Writing Well" - William Zinsser

"Dreyer's English" - Benjamin Dreyer

The problem is that everyone thinks their writing is great. You need to be willing to think it could be better. :-)