Just as an example of something that's hard, but
not because of lack of technology, real economical surplus, or engineering challenges, yet real things which are still killing millions of people each year: malnutrition, access to clean water, and treatable communicable diseases, like TBC or even HIV or COVID.
Solving those are simple tasks of manufacturing power plants, water treatment plants, fertilizer plants, agricultural machines, logistics of deploying them and keeping them fueled, and persuading people to take the fucking vaccine, use PrEP and use condoms. Money solves these. There's enough people and resources to do this.
The AGI foom argument basically says that the AGI will commandeer the economy of the size of a developed country, well, let's say Germany. (Let's pick Germany, because we already saw what that country was able to do when run by a dictator.)
Insisting that AGI can organize enough people to replace enough broken hardware while manufacturing new hardware doesn't seem that far fetched. (Again, Germany was able to increase its industrial production during WWII while the Allies bombed it constantly for months.)