What is clear from reading both the accident report and that NASA history thing is that after 60+ years of development and research, the designers still really don't know everything about how a tiltrotor flies. The accident report confirms this: The computer modeling of the aircraft behavior and required pilot inputs wasn't even close in the high-speed regime. When it began to go pear-shaped, things happened FAST!
Indeed.
and - unless I have missed something - this happened during "classic" flight mode, not transition. My uneducated guess would have been that this part of the flight envelope to be well understood and modeled.