John Kenneth Galbraith was hardly a "leftist opinion writer". He was one of the leading economists and thinkers of 20th Century, and an advisor to JFK..
Reagan's polices didn't "lift all boats". They swamped the American worker, destroyed his union, and left him with no raises for 40 years. His policies doubled food stamp usage in the first 2 years, and that's AFTER Reagan changed the qualifying criteria to make it harder to qualify. The rate of poverty went from 11% to 15% under Reagan.
Even Reagan realized his policies had failed after the stock market crashed and unemployment hit 6%. He spent the back half of his second term overseeing the greatest tax increases in US history. Sadly, Republicans didn't learn the lesson because they keep cutting taxes, increasing the deficit and crashing the economy every time they get the White House.
When Reagan took office, the working people owned 5% of the wealth of the nation. Today it's 0%, and they're dependent on government handouts.
Reagan didn't "lift all boats". He began the greatest transfer of wealth in world history. Wealth didn't "trickled down", it trickled up. From working Americans to the wealthiest, and that continues unabated to this day.