You're right it's pretty challenging but 27+ months and 300+ engineers challenging? I would have suspected to take half the time which makes me wonder what their architecture originally looked like and what they've been doing for so long.
The migration project has taken 27 months with 300 staff, about 8100 man-months, with apparently little to show for progress. Lots of people in a project with no tangible features, like a blob.
I would say Conway's law fits perfectly.