Propsforever, the report actually goes a long way to answering your questions. I don't believe you have read it too carefully.
You appear to be forgetting the effect of the sideslip. At 30 degrees of sideslip, there is considerably more drag, considerably less lift and somewhat reduced thrust. As stated in the report, the ATSB were unable to quantify each of these effects without going to considerable engineering and modelling work - due the manufacturer not possessing the necessary data.
You claim that you could hold the rudder forces for a minute. Have you ever tried this in a real King Air or a simulator? You could have just read what the test pilot said. He said that the forces could be held for only a short time, after which the "leg gave out" and the aircraft became uncontrollable. He certainly did not say anything about being able to get the aircraft back onto the ground. He did say forces were evident before rotation, however, and that the takeoff should have been aborted.
And why the takeoff roll extended? The report suggests a highly probable scenario where the pilot, nearing rotation speed, notices the rudder forces required, becomes suspicious and transfers his attention to the engine instruments, with the result that he goes past the rotation speed by a few seconds.
Have another read.