I always use ogres as my comparison point for fireball, when you first get fireball, this is how the average damage of a 5th level fireball compares against an average ogre.
- 2e: 5d6 (17) vs the ogre's 19 hit points (35% chance to save).
- 3e: 5d6 (17) vs the ogre's 29 hit points (20% chance to save assuming a DC of 17).
- 5e: 8d6 (28) vs the ogre's 59 hit points (25% chance to save assuming a save DC of 15).
The highest chance to save is actually 2e, but failure means they are 1 hit away from death by a warrior, success means they might die after two hits.
3e they have the lowest chance to save, but even if they don't they are still a couple of hits away though a power attack might take them out. 5e, they take the most damage but if fail the save, they still have half their health left and will likely survive the first couple of hits at least (warriors of course being able to strike twice a round).
Fireball has basically become less scary as each new edition has come out; however, in each edition it is admittedly still good at clearing out the trash mobs, those 1 or 2 hit die mobs that are assaulting the party. It's just that in 2e (and earlier), a fireball was much better at taking out higher hit die mobs due to the lower hit point thresholds of that edition.