AI research is hard. It's not clear to me that a serious, global ban on AI would only delay the arrival of AGI by a few years.

The other thing to consider is just what the ban would achieve. I would expect it to lower the 75% chance by giving us the opportunity to go extinct in another way before making a mistake with AI. When I say 'extinct' I include (d)evolving to an equilibrium (such as those described by Robin Hanson from time to time).