Imagine if Alphabet was broken up, Google search can still afford to run a research lab, as can youtube.
The problem I think is how easy it is for large companies to acquire smaller companies. It's how they expand or enter a market, they refuse to be bothered to bootstrap a new org-unit. They just devour smaller, innovative and creative companies. Look at Google, they couldn't be creative and patient enough to compete with youtube so they gulp up youtube. It's the bigcorp M.O.
So why bother with R&D when you can just buy a smaller company that does R&D, tests the market and builds a brand for you? My answer: you will suffer from brain drain.and reputation loss,when you buy a smaller company,consumers assume that brand is now dead. You become a cemerery of dreams and ideas. You become an IBM,HP,Xerox and AT&T. Once the damage is done it becomes nearl impossible to recover from. I like IBM as the best example, they are doing superb amounta of innovation even today but look at all their initiatives lack any traction or competitive edge. They have a ton of smart people working on brand new areas of tech like quantum computing,but their reputation and overall culture has not been great. They've been declining consistently. Look at yahoo, yahoo!! They had legitimate means to compete with google toe-to-toe,they relied too much on aquisitions as did Verizon that recently aquired them for a meager $4B.
In the end I blame all this on how publicly traded companies prioritize quarterly profits as opposed to multi-year growth. Acquiring bumps up the stock value for a while, spending billions starting from scratch competing or developing a new concept is risky so stocks go down.