In the modern era I would agree. Certainly tactical nukes and even the bunker busters will take out any conceivable fortification.
But cities can be considered a type of fortification, and are certainly much easier to defend than open ground.
And during the period from WBTS to WWII, fortifications were ubiquitous, because technology made one soldier in a trench the equal of 2 or 3 (more during early years of WWI) assaulting it. Later tech of course eliminated some of this advantage.
IOW, while fortifications cannot likely be held forever, they can certanly make it a lot easier to bleed the enemy.
Certainly one of the most successful defenses of a fixed position was by the British at Rourke’s Drift in South Africa in 1879.There is some merit in compelling your enemy to come to you into a killing zone. And then there’s the nightmare of it too. Fort Douamont at Verdun was truly horrifying for it’s French defenders. Their air supply was quickly cut off from shelling and the men literally began to suffocate, their observation posts were knocked out, essentially blinding them and finally a large caliber German shell found the ammunition magazine and bought the roof down on the men, entombing them. Rommel had right when he said “Movement brings victory’’.