I don't have a problem with the corps being more powerful than the national governments, but I find it hard to believe they can cause the UCAS Blackouts without a fight. It is basically public knowledge that the Corporate Court caused the Blackouts; they started immediately after the UCAS revoked the BRA in their country and the UN failed to send relief until the UCAS capitulated to the CC. That is all public knowledge in-universe and there aren't many other possible interpretations.
It is stated that England did their best to help the UCAS and they didn't get Blackouts, I don't remember which book that's in (I don't think England helping the UCAS is in Margin Calls; I couldn't find it there), but that means this weapon is limited. The Court also shoot themselves in the foot every time they use this weapon, as repairing the Matrix afterwards is a hassle. With the bullshit Ares in Cutting Black, the Megas are actively antagonizing the national governments. And now that the DSW is over, the Megas are also in an especially weakened state with important people having had their faith in their companies shakened.
Essentially, I can't imagine this not leading to the national governments kicking the Court while they're down. It might not led to all-out war, but I'm sure the governments will take this opportunity to take some power back. Maybe we'll see state-owned companies getting AA status. What does everyone else think?