With hold fire (like the ghosts have), tanks may continue to be a part of a battle against broodlord infestor. With being able to manually focus down what you want (infestors, infested terrans), and not having the tanks shooting at each other will make it so that Zerg has to be careful with infestors, and not put them in range of the tanks. Thus vikings + ravens are safer against fungal. They are also safer to infested terrans, as tanks are quite effective vs them. Queens as well can't just enter the battle and shoot away before the tanks are dead.
A major problem with broodlord infestor against a meching terran is how tanks are just made irrelevant. This is not good design, they should continue to have a role, even in the major battles.
This also makes the game HARDER. It encourages micro from both the Terran and Zerg player. If the terran doesn't focus fire, the tanks will do nothing. And if the Zerg doesn't keep an eye at the infestors, they will actually die.
This solution doesn't involve a NERF. It's a BUFF. Which is a good thing. And it creates awesome situations, where blunders can be made from both sides with terrible consequences. Such as moving all infestors in tank range, or having your vikings clumped and getting chain fungaled. At the same time it makes late game battles LESS volatile and chaotic, and more micro oriented.
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