Read the report on the Fine Air DC8. The cause was determined to be a catalogue of loading errors by an unsupervised loading team resulting in an incorrectly loaded aircraft. The report is readily available on the internet. Then put your suggestion of a "load shift" to any experienced loadmaster and you will get a very short answer - where is the load going to shift to when the aircraft is fully loaded??!!
IF load shift was a factor, the aircraft would need to be half empty to start with and everyone assumes that the cause would be the load moving aft. On the MD11, an extremely nose heavy trim would in fact have the
same effect on take off as the eyewitnesses describe having on the Avient MD11. By extremely nose heavy trim, I mean outside the envelope, and before you ask, if you mix lbs and kgs and lb inches and kg inches within the same weight and balance mechanism, without understanding the consequences, this WILL happen. Raises a lot more questions now doesnt it? The MD11 is not a DC10, it can be a lot more unforgiving and needs a lot more close attention to load sequencing and supervision. Too many people think of it as just a bigger DC10 and it isnt. How many DC10 Loadmasters have I seen transfer onto the MD11 and get caught out. To illustrate this point, do a web search of aircraft sitting on their tails and see how many of them are MD11's. In Avients case they only had the type for a week so you have to ask how much experience there was within the organistion on this type, excluding the flight deck crew who were highly experienced pilots on the MD11.