The problem with the Kessel Run claim is the fact that Han says the line as an answer to a question about speed. Obi-Wan says he is looking for passage on a fast ship. Han asks, “Fast ship? You’ve never heard of the Millennium Falcon?” Obi-Wan replies, “Should I have?” Then Han says the famous line, “It’s the ship that made the Kessel Run is less than twelve parsecs.” A parsec is a unit of distance, and distance is distance. You drive 60 miles; it could take you three hours if you go 20mph or one hour if you go 60mph, but you still travel 60 miles. Speed is determined by the relationship between time and distance. Again, without knowing how much time it took Han to complete the Kessel Run, the comment is an attribute to his navigating skills and not the performance of the ship. If Han has said, “It’s the ship that made the Kessel Run in 11.7 parsecs in 3 days,” then the speed the Millennium Falcon could be determined, giving Obi-Wan an actual answer to his inquiry.
Taken by itself and not as an answer to a question about speed, the claim about traveling the Kessel Run in less than 12 parsecs is not a ridiculous statement. There are many different routes to Kessel, and each route is a different distance. It is like when you use Google maps, and you are given three suggested routes from your location to the destination. If Han took the most dangerous course, then he could have made the Kessel Run in less than 12 parsecs. However, using this boast as an answer about speed is the source of the problem. Han could have been trying to test Obi-Wan and Luke, gaging their response. The more informed the passenger, the less of a price hike he could get away with. Or the line could be an example of poor writing by George Lucas. All Lucas needed to have added is time. With just one extra detail, then the debate about the line could have been avoided.