Whatever Gvl is and 1vs1, these are not true Diplomacy, they are variants of the basic game. The statement that this boils down to luck is flawed. I asked what game does not boil down to nothing but luck? How about life itself, you want to make that claim as well?
It would seem to me that such a statement would be made by either someone who does not understand the game or someone who plays poorly and can not accept their deficiencies and want to blame their poor play on chance. Why is it we have people that play better than others? We have people here who win more often than others, we have that on every Dip site, we have it in real life FTF tournaments, if this were a game of luck, then rankings would be remarkably similar but that is not the case is it? "Luck" is random and nothing in Diplomacy is random aside from power assignment. You make your own luck by writing others, influencing others, etc. A bad player or a poor sport who can't accept reality, can't accept they are not as good as they think they are will call it "Luck", people nowadays can't accept responsibility, can't own up to anything negative about themselves and they blame others or blame "luck", anyone/anything but themselves.