How many Meteor Swarms does it take to kill 100 hobgoblins before they can shoot you full of 100 arrows? How will you deal with the second hundred hobgoblins half a mile away?
...why are you mentioning Meteor Swarm? I was using "AoE" as an acronym for "Area of Effect", not for "Meteor Swarm".
Diamonds are also one of the better non-stick surfaces in the world.
Gold's ductility- it can be worked in to sheets mere molecules thick using bronze-age technology- has been valued for thousands of years.
And that engagement ring? Well, as someone who buys a lot of them second hand, I can say they DO retain a value in the aftermarket. Even the crappy ones are worth...well...their weight in gold.
FWIW...
An engagement ring on the other hand, is bought for obligation and bears no resell value, at all.
Actually gold is pretty rare: http://www.bbc.com/news/magazine-21969100The worth of gold and diamonds as jewelry in modern days is almost entirely down to intensive advertising campaigns designed to increase desire for something that is neither as rare nor intrinsically valuable as people think.
Chain Lightning ("I won initiative and killed 4 hobgoblins with a 6th level spell! Yay! And so did all of my party mates! Now we only have to survive 84 arrows to the face instead of 100!" Edit: N.b. Chain lightning is 6th level, not 3rd.).
So it is. My mistake, I meant Call Lightning, which is third level. AoE *instant* spells aren't the tool for the job. AoE *duration* spells are the better artillery equivalent.
If, for some reason, a) you're in a situation in which all 100 of them can fire directly at you (which means you're not properly using all your sensory and mobility advantages), and b) the occasional hits are somehow more than a curable annoyance despite your False Life, your paladin buddy's Aura of Vitality, etc., then use Hunger of Hadar instead. Their first rank isn't gonna deliver aimed arrow fire from within it, nor can the ranks behind them, since it blocks LOS. Follow up with cantrips, because the side with infinite ammo has an advantage in a battle of attrition by mutual blind fire.
It's not just the hobgoblins you can zap *on the first round*. It's how many every round, for the spell's duration, and the morale effect. Moonbeam, Call Lightning and Hunger of Hadar are *at least* as terrifying as a modern mortar barrage. When you incinerate 10% of an attacking force, the remaining 90% notice. Units which keep attacking after 25% casualties are notably stubborn. If you were hobgoblin #26, in a force which numbered 100 a minute ago and is now down to 75... would you feel lucky?
Sure, you play your other cards too. Your AoE-Duration spells prevent them from using close formation, and thus your warrior allies can mop them up in detail, and so forth. AoE-Duration spells are still game-changers against horde foes which can't survive 2d10 damage; much more so than Wild Shape, Action Surge, Sneak Attack, etc.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.