Quite the opposite, they were two of his best films. Remember, Christopher Hitchens is a brit, and it has to be looked upon in that light.
They were indeed, but that doesn't make them a) good or b) historically accurate. See here for an excellent breakdown of Braveheart's ahistoricity.
And as for The Patriot: the scene where the British herd civilians into a church in South Carolina and then burn them alive is based on a true incident. It happened in 1944, when the Nazis murdered 642 people (including 205 children) in the French village of Oradour sur Glane.
By transposing Oradour to South Carolina, and making 18th-century Britons the first moderns to commit this particular war crime, Gibson put his imprimatur on something unpleasantly akin to Holocaust revisionism. He starred in a film that inoculated audiences against the unique historical horror of Oradour and that implicitly rehabilitated the Nazis. As well as insulting a lot of British people - and history teachers!
I thought the Patriot was awful. And Braveheart was a long torture film. Gibson hs a "crucifixion" complex and sees himself as the guy on the cross. Same thing in Lethal Weapon - the long torture scene.