..like they could have handled all of Sauron’s army by themselves if only they had arrived earlier.
Given how potent a fighting force they proved to be, it seems odd that enlisting the ghosts’ help wasn’t part of Gandalf and Elrond’s plan from the beginning. It seemed like an afterthought.
Plus if they're already dead what's the risk? Agreed, a bit of Deus Ex Machina.
It makes me think of a phenomenon that exists in movies that thankfully we didn't see here. In some films we see a force that initially presents as insurmountable when the story benefits but eventually prove to be absolutely defeatable, again when the story benefits. It's maddening.