Buybacks are the correct option for these companies, because otherwise they would be burning money on stupid projects or acquisitions. The money goes back to shareholders, via higher stock prices. They then need to put this somewhere, and many just buy more stock. Stock valuations rise(lowering expected returns), and this causes more sophisticated investors to leave the general public markets and look for opportunities elsewhere... resulting in the 'real investment' that you want. Large, established, public companies are NOT the right vehicle for this investment to happen through.

Also, you need to read through the fake news headlines a bit. The top 10 companies are responsible for a disproportionate amount of these buybacks. Smaller companies probably have ways to use the extra tax cut money. Apple may not have needed lower taxes, but pretending like all companies are in Apple's fortunate financial position, and hinging your argument on that is like arguing that lotties are the best use of money because you won the lottery.