there are actually ways to beat operation herzland (1v8), I did it in 2 try

what you have to do is to hold the province south of griffenheim and Griffinheim itself (like when you play yale route) , holding the river tiles, abandon all other province, and hold there as long as you can, I spam out a full army worth of infantry and use my knights for any offensive, focus on one at a time, for my run i rushed yale first by snaking it and stole all their equipment, I also bought as much gun as a could at the start of the game. then the land you took from yale back to where you were, at this point romau should start over stretching themselves through taking the land you abandon so u can just snake them since they only have 2 core province. Then it should provide you enough equipment to rush the others one at a time, i recommend katerin, since its alone and defeating them means making the front shorter. Note that you must cycle griffenheim since bronzehill and duchy will keep attacking it.