The difference between theoretical math vs. applied math, is that one gives you spherical cows in a vacuum, while the other needs to take into account valve intake shapes and positioning so they can relight the reentry engines while fuel is experimenting those centrifugal forces.

"Will and dedication", is what SpaceX is doing right now: getting stuff explode until they manage to account for all the variables you need to plug into the formulas... and this is just for the easy rocket science.