Unless most tech workers are 50+, they would not be saving the majority of that money, but rather investing it in the stock market.

Investment rates and savings rates go hand in hand, and taking money from the upper middle class to give to the investor class is not sound economic policy. Savings don't depress investments, on the contrary they reduce capital costs and allow for more investment without inflation. Banks don't actually keep your money on hand, they lend almost all of it out.

I don't know Keynes well enough to know if your take on his work is valid, but I do know that parts of his theories were found lacking 50 years ago in the last bout of stagflation.