I realised that some have an old view of the state of the Greek railway network. Which is understandable, is has been in really bad shape. But in the last 10 years or so, a lot has happened. The Athens-Thessaloniki line has been upgraded and electrified which has cut the travel time between the cities to 4:10, and earlier this month they received the first of a number of refurbished trains that will bring down the travel time to 3 hours.
The Athens-Patras line is currently in the process of being upgraded, from a single track narrow gauge line to a modern electrified double track. The upgrade has reached Aigio and will eventually reach Patras as well. What the plan is after that I don't know, but don't dismiss trains in Greece.