1746 pages that fail to explain why a deck cleared for up to 4 x H-1 type helicopters (ie spots 3,4,5 & 6) or a normal clearance for up to 2 x V-22 type aircraft on the larger spots (1 & 2, which straddle the space for the 4 smaller spots) somehow became suitable for 5 x H-1 types on deck and then expect a V-22 to land on what remained of spot 5 - from a particularly non-standard approach angle.
It was a bit of a surprise for the investigation to claim that the 5 aircraft on deck were all folded, when 2 were still fully spanned - including the UH-1Y on spot 3 that was visible on the video. As an aside, the types on deck should have had their blades folded and fully secured to avoid damage from V-22 downwash but 2 were not. They had got as far as socking the tail rotor on spot 3, before it was all sliced apart. The 4-blades just take longer and more equipment to secure than when the aircraft had just 2; but who in command wants to hear that.
Returning to the non-standard approach angle I mentioned above (at around 40 to 45 deg off to starboard rather than over the stern) this is a particularly tricky thing for a V-22 to do. Even when operated from the comfort of solid ground the V-22 has a relative airspeed limit of 20kts from about 30º off the nose; beyond that and your are in the 'Avoid' arc and ultimately the straight-to-crash arc.
Things are considerably more tricky for boat ops as this 'relative' airspeed limit can be eaten by the boat / wind alone or by a resultant of boat plus aircraft approach and manoeuvring airspeed. Even without all the airflow oddities around a rear deck and the differing ground-effect patterns from the V-22 rotors and residual nacelle thrust, you can get into difficulties even if you think you can stay out of the 'Avoid' zone whilst reasonably heavy. The 'escape' manoeuvre requires space to the front to accelerate into, which is now occupied by helicopters, people, equipment and the ship itself. If you make lateral inputs instead you induce a thrust imbalance that will reduce both the total thrust available and drop a wing / nacelle.
How long had this been going on... enough for every ship of this class to have scorch-marks at an odd angle outboard and aft of spot 5.
This was a serviceable aircraft, with a competent crew, in relatively benign conditions, by day and on a training exercise. The boat had a full hangar, an overly full deck, aircraft not fully secured and folded, plus the habit of trying to squeeze a V-22 on a spot that was large enough for a Huey.