It's worth noting that William Pitt the Younger was well ahead of George III on the matter.
I think overall George III didn't do that badly. He lost the 13 colonies, to be sure, but he also supported James Cook, which brought him Australia and New Zealand, kept Canada, and had the amazing good sense to appoint William Pitt the Younger as his Prime Minister, which did an amazing amount of good during the wars of the French Revolution and Napoleon. He also gets a gold star in my opinion for standing up for John Harrison when Parliament was trying to cheat him for solving the longitude problem.
My overall impression is that George III was supportive of science and technology, which did a great deal to make Britain more powerful in the nineteenth century. He certainly has his negatives (the American Revolution, opposing Catholic Emancipation, going mad), but he was the best of the four Georges, and I think overall did more good than harm.