Right, and you can land on the moon with basic newtonian mechanics. The are millions of devils in the details but for a person to decide how big a rocket to build and whether it could land vertically after a payload of X that needs a delta-V of Y, its easy napkin math to prove feasibility.

Executing it is then one of the hardest things people can do but SpaceX had all the best people at the time.

You can claim anything is easy this way. Just take the easiest subset of a problem, and show how easy it is. I find that to be a pointless argument.