Your canon story doesn't leave you dead in the middle of fights as often as you might find yourself. Additionally ghosts don't do that hover mechanic over their guardians bodies. A ghost primarily stays out of sight as much as possible to ensure they can rez their guardian. There's a really cool lore entry with either Saint-14 or Rezyl Azir where they actually let themselves get killed so that they can be rezzed in this massive eliksnis grasp to surprise and murder him as a means of scattering an overwhelming fallen force. I'm seeing a lot of confusion in your post responses so I wanna inform you that first of all, ghosts aren't that hard or special to kill. That's why they stay hidden. This was a big confusion for a lot of people when Cayde's ghost was killed with a devourer bullet in the forsaken campaign. For anybody that lore dives, the devourer bullet obtained by the scorn barons was intended for Cayde because you need crazy evil guns and bullets to perma kill light bearers. Devourer bullets have the potential to kill guardians regardless of our affinity to the light. Think of it like a bullet that can rend a person's light like Crota's sword. That's why the original thorn was so scary. The sniper baron shoots caydes ghost because she comes out in the open under the impression that she is safe to heal cayde. Baron kills Cayde's ghost so they can get a more satisfying revenge on the already beat to shit cayde. Ghosts are actually just the floating eyeball with shells comprised of materials from their surroundings etc. (why they are so customizable)

From a lore standpoint, our ghost doesn't typically pop out to assist/revive us unless absolutely necessary; I don't think we've ever died on screen either so the situations we die in lore-wise as opposed to the actual game are probably (very likely) different. Also, it's very much possible to detain and/or destroy them without paracausal means. Most recent example of a ghost dying I can think of is Felwinter shooting and destroying a warlord's ghost, and he obviously wasn't darkness enhanced. For incapacitation, there's the Slap Rifle that incapacitated Sagira during CoO as well as Spider selling a live ghost in an anti-transmat cage in Joker's Wild.

Like someone said below, few weapons can kill a ghost i think. One ex being what happened in forsaken, that bullet was made exactly for THAT purpose. Can’t remember the specifics of it though

Easy explaination. Even if they hit our ghost it wouldn't do Jack shit. Caydes ghost was killed by a thorn round, sagira was killed by hive who are notorious for draining and killing ghosts.

<Lore-wise, because we have plot armor. For gameplay, because it'd make every single zone an instant Darkness-zone and that'd just get real annoying after a while (see raid revive tokens).>

Ghosts can only be destroyed using Devourer bullets. Same type of bullets the Hive make/Thorn uses. Kind of hard to come by for your regular Dreg/Goblin/Legionary.