It only seems far when you are coming from the Haunted Mansion and have to fight the crowds to get out of Liberty Square to get back to the hub. But, in terms of actual distance, it is not far at all.
Casey's offers online ordering through the
MDE app. You'll save yourself LOTS of time in line by using online ordering.
Be aware that the tables to eat outside are a bit of a zoo. Across Main Street, by the Plaza restaurant, are more outdoor tables and chairs. You may find it easier to snag a table there. When my wife and I want to eat at Casey's, we find a table over by the Plaza, then order through the app. By the time we walk across Main Street and get to the order pickup window (which takes about a minute), the food is ready to pick up. After eating the hot dogs, we're then ideally situated for ice cream at the Plaza.