Putting all your eggs in one basket with a handful of extremely large companies might not be a long term winning strategy. Companies fail eventually. Big companies are no exception. When they do, things get ugly.
The FANG companies are great at hoarding wealth but not so great at converting that wealth into new things. You need small, nimble companies for that. And not necessarily the VC funded Silicon Valley variety. Which of course is basically the FANG companies (and their clique of wealthy investors) trying to own and monopolize the future.
A dynamic you see in Germany where I currently live that I find very interesting is that of family owned businesses thriving and adapting to modern times every few decades. Germany has a lot of very wealthy families and some of these businesses are multi billion euro companies that you probably have heard off and there are loads more that you may not have heard off that are also worth billions.
Lately some of these companies are discovering the virtues of going online with their business. You might argue a few decades too late. But we are talking real businesses, with real markets, real customers, and real profits, real products, etc. They'll be fine. They are simply adapting and integrating commodities like the internet and making it their own. In some cases they simply skip a few steps and fast forward to what many other companies might still consider science fiction. Some of them make it work and prosper, some don't. And they disappear or get replaced by something more successful. It's organic, highly adaptive, chaotic, and competitive. You might even say that this is capitalism actually working.
Some of those commodities are provided by the above mentioned FANG companies. But how crucial are they really long term? Amazon is nice and all but it's basically just a logistics company with a side business of running cloud based services (or the other way around). I've used both and it's fine. But I also use competing services and products. Amazon being big doesn't make them better at what they do. Often it's the opposite actually. Bureaucratic, slow to adapt, not able to tap into opportunities when the payoff isn't measured in billions/trillions, etc. It takes more agile/nimble companies to do that. You find these companies all over the world.