I think you are taking this way too personally. They are a very small company and they work hard. With Dinafem and Dutch Passion MIA they are easily one of the very best guardians of fine autoflower genetics out there. Since I graduated from beginner grower, I have never have germination issues with Mephisto seeds, or really any seeds as long as they were fresh and or well stored.
To answer your question about the humidity dome, I just cut the middle out of the dome from an old cloning tray. Then I just overlap the pieces to fit the size of the pot. I also only use it in the winter when the humidity it very low, less than 30% RH. And when I do use it I place a small hygrometer inside the dome and I remove it as soon as the rh gets above the mid 60s. I think rh being too high is what ruins more germinations than it being too low. If the rh is too low seeds will almost always still sprout if they are viable, just start a bit slow. If the rh is too high then the seeds get water logged as soon as they crack. They must be damp, but not wet and warm but not hot. Seeds are all like a little Goldie Locks, they need it to be “just right”. Anyway, I think your problem is possible caused by keeping up humidity too high, and not the other way around.
Good luck!