Boards love a clean-sheet story. Operations cannot afford one. The systems that print money are rarely the ones engineers want to touch.
A strangler-fig program is slower to announce and faster to de-risk. You put a facade in front of the old world, siphon one capability at a time, and keep a parity suite so finance cannot be gaslit.
If you cannot describe the first slice that creates value in ninety days, you do not have a modernization plan. You have a wish.