It is true that Washington was also a slaveholder, but that is where his resemblance to Lee ends. As Matthew Yglesias pointed out in Vox, we revere Washington today because of his many accomplishments on behalf of the nation that had nothing to do with slavery. He was the military leader in the Revolutionary War, he presided over the Constitutional Convention in 1787 and, perhaps most important, he established the precedent of peacefully leaving office at the end of his term.
Lee, in contrast, had virtually no achievements other than the military defense of slavery, which led to the deaths of hundreds of thousands of Americans. If Washington is remembered despite his connection to slavery, Lee is remembered only because of it. To be sure, Washington's slaveholding is, and must be, an indelible stain on his reputation. Lee, by contrast, would have no historical reputation at all if he had not committed treason to defend human bondage.
The lives of Washington (1732-1799) and Lee (1807-1870) did not overlap, and they were divided by a crucial inflection point in American attitudes toward slavery.
http://www.chicagotribune.com/opinion/commentary/ct-george-washington-lee-slavery-20170820-story.html