Poor ranking university

Hello everyone,
I am currently studying pure math at the Kapodistrian university of athens which, albeit known for its difficulty has horrible rankings. Hell, even the entrance exam compares to the STEP exam which is considered top level and gets you into oxbridge. I didn't make it into the IMO (which is pretty bad) but I have raised some serious capital in the market for my age (which I've been told won't help you break into a firm). We do know someone in the same boat who landed a remote 90,000£ data analyst position outside finance which would still be fine because I live on only 600€ a month here but is it really viable to pursue a PHD for a good chance to break into a firm? I'm not really that scared of interviews I'm reading through Heard On The Street Revised and I'm not intimidated, I just think I will be a weak applicant. Let me know what you think.