I didn't pretend anything. Even if your property is taxed at €500k although it's worth €250k, you are still paying very little compared to Denmark. And actually, it is close to zero.
Many of my friends, all middle class, pay €5-10k per year in property taxes for what is really modest 100-150m2 apartments or houses in or around Copenhagen. Are you anywhere close to that in Athens?
Yes, easily more than €5k/year for a 120m2 house. (not me actually, my parents, but I doubt they lie to me about how much they spend)
Like others have already mentioned in other threads, land & property valuations are defined by the state, and are way inflated and unrealistic. On top of that, there's all these ridiculous things that contribute to the property tax, like how many streets neighbor the building, etc.