My PhD is not my magnum opus (burnout vs mediocrity)

I'm (27m, 1 bsc, 2 ma, 1 year mandatory army) in my first year of my PhD (Social Sciences, statistics + fieldwork) in Greece. With no funding, I also work 40 hours/week in order to survive; I was freaking the f out. I had it all. I gained weight, zero social life, no money, no sleep, and I was always exhausted. I thought of giving up, thinking there's a class difference or something because there's no way my colleagues have so much free time.

Turns out I had it all wrong, or at least that's what my advisor told me: "Your PhD is not your magnum opus, it's just a way to learn HOW to work in an academic environment. Don't be so hard on yourself."

I never considered myself a perfectionist, but I can't stand the thought of finishing a PhD knowing that I could do so much more. Even though I felt better after the conversation with my supervisor, now I feel even more lost. So, the next three years of my life will just be a formality? A seminar on "how to navigate academic environments"? How do you guys cope? What am I doing wrong?