Another interesting angle is that in the new interface, they had to add a dropdown menu to control the amount of padding used on UI elements (compact, cosy, comfortable). Had they gradually moved from compact to cosy, then to comfortable over a longer period, the need to provide an option might have been removed entirely. So some of the complexity avoided in having incremental changes over a fixed term has instead become software complexity needing maintained over a potentially longer or indefinite period.

In either case, a gradual transition would avoid the need for all this. For me, the two biggest gotchas with the new design was the text->icons change and associated relocation of some buttons, and the border change. Had the text->icons change been introduced distinctly, and allowed to stew for a few weeks - months, then the border size changed from compact to cosy for a few months, I possibly would have had no reason to complain at all (the amount of adjustment/effort required for each individual change is amortized over time, and by the time a new change appears, my comfort level has already returned to maximum for the current state of the UI).