Straight answer

Is a GHIC enough for Europe?

No, but it is worth having alongside insurance. A GHIC (the successor to the EHIC) gives you state healthcare in the EU on the same terms as a local, which can mean paying what a local pays rather than getting it free. It does not cover mountain rescue, private clinics, or getting you home, which is the expensive part. Carry the GHIC, and hold proper travel insurance too. The card is free from the official NHS site; never pay a website to get one.