Google uses page loading speed as one of its ranking factors in search results, especially for mobile searches. A page that loads slowly for its Greek visitors is at an objective disadvantage against competitors with faster hosting.
Beyond raw speed, a server based in Greece also reduces the risk of errors or timeouts that can occur when data travels long distances across multiple networks.
Combined with basic SEO practices — proper titles, unique descriptions per page, and clean, fast code — local hosting gives you a small but consistent edge in a market where most of your competitors are likely hosted in a similar way.