The problem isn't multi-target infernos, the problem is the OP's inability or unwillingness to adjust. All updates change the game. I am upgrading my freeze spell now, which works great on multi-target infernos (yes yes...I know...not available to th9s...). Golems are also back in vogue; try them vs multi-target infernos and see what you have to complain about!
Moral of the story: instead of expecting the same strategy to work the same after an update (e.g., balloons and minions), be prepared to adjust. Use different armies or spells, deploy differently, target other types of layouts.
Thank you supercell for keeping the game fresh.



