My opinion is that getting a degree in English will help your writing. But your personal writing is not likely to get you a degree. That being said, keep in mind that a very successful writer is rare and has likely spent a lot of effort getting to that point. While a degree in English is not likely to pay as well as a degree in, say, engineering or business or medicine, it certainly has a lot of applicability in a wide range of occupations. You'll also be free to pursue your personal writing as well. Also, pursuing a degree in English doesn't prevent you from also minoring in a wide range of other fields. I personally went from medicine to engineering while taking advanced classes in various forms of creative writing, and all of that proved valuable throughout my life. Not to mention being exposed to other aspiring writers from whom a learned quite a lot and got a good perspective of the incredible competition out there.
I've been a professional writer for a few decades now, but I've also written (mostly for myself) poetry, fiction, and diaries. I agree with Mark Stewart that getting a degree in English can help your writing. It'll raise the quality of your writing and your mastery of the language if for no other reason than that you'll have writing assignments and that someone with experience and knowledge will be critiquing that writing.
Becoming a working professional writer (journalist, technical writing, etc.) is easier than becoming a successful fiction or poetry writer. It's a different world, really; for the latter, you'll probably find that you have to do something else to pay the bills while you're trying to succeed.
My experience, and that of many people I've known, is that going to university opened a lot of pathways for them that they didn't know about before. So I'd say yes, a degree is a good idea.
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Getting a degree will provide many experiences, as well as introducing you to new people and ideas, through which you can expand your understanding and perception of your surroundings and your own writing. Working with teachers and fellow students, you will likely be exposed to new writers and genres that might remain unknown to you otherwise. You will also be able to learn from instructors who have more experience, technical skills and overall wisdom than you have at this point. Focusing on your own writing is, of course, something you should do as often as possible. But the interactions and education you will garner while pursuing a degree could make you far more productive, and inspired, when you return to the solitude of your writing space. Getting a degree is by no means necessary to writing, but you should seriously considering taking advantage of the opportunities it offers.
I think comparing these two may not be the most efficient way to make a decision. A degree in English may not make you a better writer but it will open doors for jobs, especially teaching jobs. Some employers will not care that you are an amazing writer if you don't have a degree. So, I would say, get the degree. Get a college degree that does not need to even be in English. Many writers major in psychology, history, anthropology, or a foreign language. A college experience broadens your horizons and makes you a better critical thinker. It will help your writing, too, but that is not the primary goal of obtaining the degree. However, you might be worried that a degree will distract you from your personal writing and you are correct to worry. I would consider setting time for yourself to write regardless of the pressure of obtaining a degree. Or, consider going for the degree part-time if you have a project started already that involves your personal writing. But do not drop the degree altoghether.