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.