let me add:
#1. starting a brand is a business. Doing what you love is a hobby. Making money (preferably by doing what you love) is a business.
#2. Graphic tees will never die! graphic tees have always been the staple of independent brands. Long after flannel shirts, skinny jeans, snapbacks, and whatever trend is popular now, or was popular for the last 50 years...consumers have, and always will purchase graphic tees.
In terms of doing what you love, which in my case would be 'to create a brand', entails that part of 'achieving' what you love, means incorporating good business. Moreover, if you didn't incorporate the proper business that it takes to be successful as a brand, then you are not achieving and doing what you love. Of course though, this is subjective to myself and others have varied opinions of success/brands/aesthetics/whatever.
Also, I never said graphic tees will die. They never will. I love graphic tees. I believe good brands create TIMELESS clothing that will stay in your closet for years to come. Make authentic, quality stuff that will reflect positivity on your brand and the message you are trying to relay to your audience.
Actually fuck it. Just do you.