So my group tried out story 3 for the first time, which is a very wide open scenario. I also had the pyromaniac card.
I had 4 investigators, so 4 threat per round. I started out solely using the pyromaniac card, getting to place 2 fire tokens a round.
Because the outdoor rooms are so large, I quickly engulfed the entire outdoors in flames. I made certain not to spread fire into sealed doors, but ultimately I was able to cover every outdoor room (I only stopped because I ran out of fire tokens).
This resulted in a barbaque of my players. By the time they got into the lower levels and I switched to zombies to fulfill my objective, they were so worn down I was able to dispatch them easily. What made it worse was when they got a new investigator, because they have to sit at the start location for one round they immediately took 2 damage from the fire.
I saw nothing on the pyromaniac card that says can only be used once per round (unlike many other cards that are very specific about it), but my players had a terrible experience and called shenanegians.
Am I missing something?
As far as I understand, you did everything correctly. Mansions of Madness is sometimes unbalanced and I have never won or seen anyone win while playing Blood Ties (though I came 1 round away once from a win). Some cards like Pyromaniac do not compensate between one to four investigators, respectively: it always forces horror checks when moving through and 2 damage if an investigator ends his or her turn in fire. Very rough Keeper Action card. I think the lower amount of investigators, the more likely you can win in Blood Ties. Large groups seem to die, especially from Pyromaniac.
I find The Fall of House Lynch, The Inner Sanctum, and Green-Eyed Boy to be the easier of the five scenarios for investigators. Blood Ties and Classroom Curses I don't believe I have ever beaten in any scenario. 'Til Death Do Us Part is an excellent scenario too for investigators, a PoD expansion. I enjoy also Season of the Witch. Teaching them to Keep also helps the investigators eventually understand how to fight the odds against the Keeper. The game challenges players to become veterans to the Keeper's merciless mechanics. Eventually, your players will get better if they adapt to their environment and persist till they win. Very survival of the fittest, Lovecraftian game, and requires some patience and learning the weaknesses of your opponent (the Keeper). In the end, I win about 50/50 when I play as an investigator, and I have played the game almost fifty times, for sure.