Immunity and Nullification by themselves don’t counter it at all. Even Quetzorion doesn’t get a guaranteed win.
Indo G2’s only true counters at the moment are Procera, Mammotherium, Spinoconstrictor, Tenontorex, Gemini, Maxima and Ardontosaurus. Quetzorion does well, but mind games. Same with Indom G2. I’m unsure about Dio.
Mammotherium and Procera are overpowered for what they are. They will quite possibly, even probably be nerfed, which means Procera will no longer be a viable counter, and Mammotherium… we’ll have to wait and see.
Gemini and Maxima are busted, and while they do deserve to be among the best, the fact that they are High Tyrant says something. Again, they’re likely to change.
However, these two will likely still do very well against Indo G2, nerfed or not.
Ardontosaurus isn’t the best creature to be running at the moment, since it has nothing to protect it from Thors or Erlidoms on the first turn, meaning even if—by some miracle—it wins, it’ll die on the next turn.
Regardless of all of this, Indoraptor G2 is a High Tyrant Legendary. Saying that it’s not nerf-worthy is very bold indeed.
Being better than Indoraptor is one thing. Being so much better that a new tier has to be created for you is another.