"Returning money to shareholders" is largely a consequence macroeconomic policy or state of affairs. It is, evidently, not actually a choice that CEOs currently have in practice. Dividends and/or buybacks are one of the powers shareholders do tend to wield, in practice. They want to invest more, not less.
Also, IDK if it is a common solution. Nothing is really common at MSFT-scale. A free cash flow like Google, Alphabet, etc. is almost unprecedented.
Meanwhile, I do actually think that this is better for shareholders. IMO "Synergies" is a term somewhere between euphemism and a boomerism but for the purpose of "shareholder value" it doesn't matter. At Monopoly/Unicorn/FAANG scale, there are big opportunities for synergy. Think Google-Android.
Why is Nuance being owned by Alphabet less efficient than being traded independently or owned by private investors? Why is Alphabet owning vanguard more efficient than owning Nuance?
The answer to those question can have no actual impact on reality. If the acquired business is cash generative, they can left to their devices. If the parent company doesn't borrow, then "efficiency" never becomes explicit. Explicit efficiency is relative to cost of borrowing. Implicit efficiency is implied by share prices... and at this point things get foggy.