You could take this to an extreme and compare a 17th level caster casting sword burst with 8 targets doing 32d6 compared to a meteor swarm against one for 40d6 and say theres barely any point in blowing your spell slot... you would of course be very wrong.
lets take some targets with an arbitrary health value since goblins are very unlikely to survive a fireball. And also lets set the caster to level 5 cause that's the earliest you can get access to fireball
Sword burst:
2d6 to 8 targets averages 56 in total. that's 7 damage EACH (thats the...