The burden of proof goes the other way. I've never heard a convincing argument that AGI will most likely lead to human extinction. I don't think we have enough information to make strong predictions either way. That doesn't mean we shouldn't put more resources than we currently are into mitigating AI risk. It does mean that we should be highly skeptical of doomsday claims. I posted another comment in this thread explaining why I think his claims aren't justifiable.

Edit: the idea that you can pause AI research until you solve alignment presupposes that alignment is orthogonal to the implementation details of AGI. You need to factor in the risk that pausing will hinder the necessary breakthroughs to actually implement alignment effectively.