If the balloons could be controlled accurately enough to provide internet access at a specific time each week, then you have a point. But if they fly over unpredictably, guided by the wind, then it's not going to be nearly as useful.

Utility is not binary. If they provide intermittent access to people who've never had it before, that's a huge deal.

The site linked here has a tone of triumphalism, but you can tell from other information about this project that Google is approaching this realistically. I like how Google's engineer said that they're expecting many more iterations of prototypes. No one in Africa is going to be grateful for a system that's a nonworking pile of junk. Whether or not it's worth rolling out will depend on how well it works technically, and that will become clear through testing.