The question is "What if AI is a platform like the smart phone?" and then "What are the apps that make multi-billion dollar businesses?".
so that means there are no apps built on top of search?
An app in this context is something that allows you to do something much quicker than trying to putter around and figure out what prompt to use.
There are apps that are essentially interfaces with a few frills on top.
However I do agree that based on the platform the apps you get will not be multi million dollar apps, they will be more like browser plugins. Low value propositions that does not make you rich, but maybe does well enough that you can spend your time on it.
Try to do that with a capacitive screen.