Since the PTR the Centrals have won about 50% of our games, and we also have an impassable Switzerland. We don’t have the Italy rule however.
My strategy as Centrals is going after Italy from the start with as much as possible. But considering you dont do that, I have to tell you about my friends strats.
One of my friends buys quite a lot of ships. There are certain advantages, but I wouldnt do it too much. I tend to buy a sub with GE and AH every turn. That way every ally has to consider those subs. They are never really free to move whatever whereever without expensive escorts. And sometimes you can attack a small groups of ships which messes their plans of follow-ups, etc.
Another thing I do is keeping forces occupied by sending their unit count plus one to it. Just so you are sure that those, for example, four units in a Russian province are pinned down and the territory contested. This I do with just inf, which makes it quite expensive, as they don’t do much harm themselves, but this way you cut their supply lines and get one step closer to an economic collapse.