Wow, this thread gave me a great homebrew idea.
One of the 5e / 5.5e problems is that fighting one monster or 4 monsters with the same xp budget is not the same difficulty.
Solo Monsters and Horde of Monsters are different and AOE Spells are only good against hordes, but weaker against solos.
But we could completely rebalanced the game - we would need to change the Solo Monsters (any creature bigger than medium) - but what if we did, what is suggested here?
A medium Monsters takes 1x AoE damage and Webdamage.
A large Monster takes 2x AoE and Web Damage.
A huge Monster takes 4x AoE and WebDamage.
A Gargantuan takes 8x AoE Damage.
(Multipliers I just made up, if we would go completely by the size difference, I think x4, x9 and x16 multipliers would be a little too much).
You only.limit AoE spells by their size. So a 10x10 Feet AoE spell only does maximum 2x damage per creature, for example, while a 20x20 AoE can do gargantuan level damage (x8).
One would have to adjust the HP of larger creatures accordingly. But now a large creature behaves basically like 2 medium creatures, a huge creature like 4 medium creatures and a gargantuan like 8 medium creatures.
So if we would rebalanced all the creatures with this in mind, we could balance 5e way better and make it it more balanced between solo creatures and horde Monsters.
Because now of you cast Web on 4 Orcs and than a fireball on the next round, the orcs take 8d6 + 2d4 fire damage x4, so you do 32d6 and 8d4 fire damage (average 132 damage). And large or huge creatures in the same Web only gets 8d6 + 2d4 fire damage (average 33 damage).
With my new rule a large creature would get 66 damage and a hughe one 132.
Maybe one could do that as a feat for a Big Game Hunter or something ...
It is just a crazy idea this thread got me and would mean rebalancing every large or bigger Monster ...
But it would make it a little more realistic and could fix the disparity between single Monster vs Horde Monsters.