The issue is speed-distance-time.
For example a 4000 mile trip at 18.0 kts is 222 hrs. Add say 20 miles for a diversion and now distance is 4020 and the speed required bumps up to 18.1.
Get too smart about routing and the other ships that left later will arrive earlier. The stories are always about out smarting the routers but in practice it’s like trying to beat the house in Vegas. Not easy.