I agree, Pro Firebolt Tower as it is now is the best pro boost you can get among those 5 pro boosts. A mass hysteria placed far away enough that none of your spells and your troops can reach it will be a big trouble, if you have to place 2-3 of them using this logic, you’ll have a big problem passing the base. Plus if all the firebolt tower is healed by 1 or 2 unreachable heal towers is like immortal?
Now in the dungeons there are different factors such as various types of pro/elite/war boosts, longer path, more towers/obstacles which change drastically the way we play compared to our daily routine bases. To see at 100% effectively if these mass hysteria can be a real problem we have to wait to get them.
Personally 50% i’m sure they will be.