Doing a PhD worked for me as a way to find out what I really enjoyed, by investigating all sorts of avenues (unrelated to my actual topic, which I soon hated), after aimlessly doing as I was told in undergrad and not really knowing what I wanted to do.
You don't sound like you're in the same boat at all. Maybe you have an incredible project that will fascinate you for 3-4 years, surrounded by equally passionate people; I can't tell. Equally likely you will grind it out for the last year or two, regretting not doing that start-up or something else.
Doing a PhD worked for me as a way to find out what I really enjoyed, by investigating all sorts of avenues (unrelated to my actual topic, which I soon hated), after aimlessly doing as I was told in undergrad and not really knowing what I wanted to do.
You don't sound like you're in the same boat at all. Maybe you have an incredible project that will fascinate you for 3-4 years, surrounded by equally passionate people; I can't tell. Equally likely you will grind it out for the last year or two, regretting not doing that start-up or something else.