Typically in any sort of combat RPG there's a spectrum of builds that looks like a line. On one end you have the people who put all their leveling and gear into doing MORE DAMAGE. These people are typically called a glass cannon because they do a ton of damage when left to their own devices but if they get attacked by the enemies they very quickly die. On the other end are the people who dedicated themselves to staying alive and ignore damage dealing abilities entirely. These are the tanks and they're highly desired in a game with a solid aggro mechanic. In a game with smart or even random AI they'll find they can't keep the glass cannons alive and aren't all that much use either. A more effective character in these sorts of games would be somewhere in the middle. They do pretty good damage and can keep themselves alive from reasonable incoming attacks. But they aren't as flashy so most people don't gravitate towards those sorts of builds right away.
Path of Exile has a couple of mechanics that combine to open up what I've termed the 'glass merchant' build. I don't do any damage, and I die the second anyone looks at me, but I drastically increase the amount of loot awarded to the party thanks to the way magic find and culling work in the game.
Magic find is broken into two distinct components. Improved item rarity (IIR) which makes a given item more likely to roll as a unique, rare, or magic item instead of just a regular item and improved item quantity (IIQ) which makes more stuff drop altogether. Grouping up with other people adds an extra 50% to the quantity of items dropped and whoever gets the killing blow on a monster gets to use their IIR and IIQ to modify the drops from the monster. Diablo III normalized magic find across a group so it didn't matter who was wearing the gear or who was killing the enemies but PoE has made it so only the killer's magic find stats matter. My character casts a spell that does 1-11 damage while other people are probably doing tens of thousands of damage which seems like it would be a problem getting the last hits...
Culling is a modifier you can apply to an attack which makes the attack instantly kill any enemy if they would end up below 10% health. So it doesn't matter that my attack does 6 damage... If Tom did 90% of the enemy's health and I sneak in a hit I'll kill the enemy and my magic find stats will be used!
Having a character who doesn't help kill things and spends the whole time running away from enemies doesn't sound terribly useful. (I actually summon zombies that do reasonable damage when I'm soloing but they have a hard time getting in range when Tom just kills everything before they can shamble on up.) But how much of an impact am I having on the drops compared to not having me there at all? I'm currently running at +59% IIQ and +183% IIR. Tom alone would get X items to drop while having me in the group getting the kills takes that to 1.5*1.59=2.385X items to drop with 2.83 times the chance of getting a unique on each item that drops. So if uniques are what he cares about he'll see 6.75 times as many of them if I kill all the monsters than if he runs alone.
Of course the monsters will have 60% more health and I only chop off 10% of that end result so he does have to beat through at least 44% more enemy health to get those extra drops. Even adjusting for that he's still going to get 4.69 times as many uniques with me along.
I'm also not going to kill every single monster, especially when I have to hide so often, but I can certainly kill most of the rare and unique monsters which drop the higher level stuff anyway.
Apparently there is some sort of unexplained diminishing returns which might be hurting those numbers. And some sources are saying IIQ gets shared the way it did in D3 and only IIR cares about the killing blow. I don't know if either of those things are true or how they work. But it does seem like this is at least a plausibly viable build. I can kill things (slowly) solo and I think just getting the last hits on things is a net positive to a group. I probably need to focus more of my gear on survivability so I can get closer to the fights without exploding...