There are a lot of ways to counter both ults. Ivy stomp counters both. But any stun really so knockdown, lightning scroll, etc.

Against dynamo ult there is paige ult, infernus ult, lash ult, unstoppable, rescue beam to pull others out of it, ivy ult also pulls others out.

The best way to deal with both is however sinclair imo. A good sinclair makes me as a dynamo player scared to be at teamfights because i dont wanna get my team ulted by him.