> The internet is designed to not go offline.

Only somewhat true, but the fundamental assumption is that it is operating during mostly peaceful times. You have hostile countries cutting or dragging anchors across deep sea fiber optics, you have attacks on energy suppliers, etc. The most effective attacks for denying service are to infrastructure.

> The only realistic way to do that is somehow finding a persistent DoS or RCE for every router vendor, hacking into an IXPs control systems, or physically damaging equipment. AI can't do any of that alone and I dont think it ever will.

An attack is not just limited to internet infrastructure, but even if it was: You would just have to take out a significant part of the backbone. It could be the backbone routers, the DNS servers, distribution boxes, home routers, etc, etc. Once the capacity is reduced, you may find the people themselves end up DoS'ing the remaining capacity.