For example, there have been talk about how search has shown promise in early cancer diagnosis [0].
So as you say, while Google are currently only monetizing their ad platform at the moment, they are far better positioned than Facebook to quickly find new revenue streams, should they need to.
Additionally, if you should believe that AI is going to be a huge area for monetization in the near future, then Google are very much well positioned to be a leader there - it is no coincidence that a "search" company is able to make self-driving cars or Alpha Go...
[0] http://www.nytimes.com/2016/06/08/technology/online-searches...
Sure they know what age I am, that I'm college educated, live in NY, like anime and startups. But would they know I'm suffering from hemorrhoids and need help? That I'm considering an abortion and need a clinic recommendation? I sure as heck ain't broadcasting that in my timeline.
(aside since I assume that was an example! :) [Edit: and in case you aren't, hope you do get that sorted out]
Google has better potential for growth, but it still needs to prove it can heavily monetize anything outside of search. That is, find a new business that is competitive with their search revenue, until it's too late.
Facebook's first success was monetizing mobile (which Google should have been able to do better than it currently does). Its potential to find new sources of revenue is good but not as great as Google's.
Only time will tell if either or both will succeed next. Since potential isn't as good as realized potential of course.
The real struggle lies not in the technology, but in the network-effect and branding.
Google has some products that are market leaders with heavy usage, eg:
* Search
* GMail
* Youtube
* Android
* Chrome
* Maps
* Docs
Its just that Google is unable to monetize many of them.
However, Facebook has only Facebook, Instagram and Whatsapp.
1) Instagram _is_ what Facebook was 10 years ago. Its not a new product. They just bought it because Instagram was becoming _The Social Network_.
2) Instagram and Whatsapp were bought acquired.
What I'm trying to say is that Google is unable to monetize many of its products. And if online advertisement gets doomed, it would have to look for other business models.
But it _does_ have a very diverse set of products that people love.
What does Facebook have? and when was the last time they created something people loved?