Read some history. Being stationary is not necessarily a disadvantage compared to being mobile. For reference, see static defenders:
Battle of Thermopylae (480 B.C.)
The Alamo (1836)
Battle of Rorke's Drift (1879)
Battle of Wake Island (1941)
Battle of Monte Cassino (1944)
And Mobile defenders:
Battle of the Little Bighorn (1876)
Battle of Isandlwana (1879)
I do read. Extensively. I may be picking nits here but:
The Battle of Termopylae was a tactical defeat although it achieved its objective as a delaying action enabling the eventual final defeat of that particular Persian campaign. In any case, they fought there by choice, not because their baggage train bogged them down.
The Alamo was heroic, but a defeat. And a defeat with debatable tactical or strategic purpose. It seems to have been more of a "member" measuring contest. Sun Tzu wouldn't have liked that. And I say this as a former resident of San Antonio, Texas at a young enough age that I had to take Texas history in Junior high. Again, the spot for the battle was picked by the defenders. Never been sure why.
Rorke's drift proves MY point, not yours. The British were tied down by their duty to defend the hospital and supplies there. They would presumably preferred not to have engaged the Zulu's at such a disadvantage, but had to do it anyway.
Wake Island was another defeat. By a garrison that did their best, but was unprepared for the assault. Failure of planning and leadership. Heroic, but avoidable. (I'm a former Corporal in the USMC too).
Monte Cassino was a defeat for the defenders, albiet at huge cost for the attackers. I'm not very familiar with that one.
As to the mobile defenders. That makes MY point again. Both your examples are defeats for the defense (in Little Big Horn the 7th was initially on the attack but badly underestimated the opposing force and the roles reversed in the course of the engagement). Don't defend. Be strong enough that you don't get attacked, or be mobile enough that you're not there to attack. That is the essence of Sun Tzu.
Defense is always a last resort, or a mistake. If you really want to interpret strictly I'd say FIGHTING is usually a mistake, unless it's the only thing left after all other means are exhausted.