Since this is becoming a crux of some of this debate, we want to dig a bit more in the details.2e. The new damage cap became 10 dice, capping out in damage when the wizard reaches 10th level. Still likely to kill anything it is thrown against as 10-60 (35 average) damage is still a lot of damage when targets typically have a handful of d8s for hit points, no constitution bonuses added for monsters. For instance, an ogre in 2e has 4d8+1 hit points, that’s an average of 19 hit points, a 6th level caster would be likely to wipe out an ogre and his buddies with a single fireball dealing 6-36 (21 average) damage.
3e. This edition kept the 10 dice damage cap but now, since monsters all had the 6 ability scores as well, they could add in their constitution bonuses to their hit points. Now an ogre has 4d8+11 hit points (a 15 constitution and the toughness feat for a total of +11 hit points) so that their average hit points are increased to 29. Meaning that the wizard now needs to be level 9 before they can be confident that the ogre is destroyed by his 9d6 (9-54, 31.5 average) fireball. 9th level means that the DC for his fireball spell is likely going to be 17 (with an 18 intelligence) so the ogre with a +0 reflex saving throw is likely going to fail and take the full brunt of the fireball.
2e. Alright if the fireball is 6d6, there is a 72.06% chance you will do enough damage to one-shot them, IF, they fail the saving throw.
If they pass the save: Its 0%.
I have no idea what 2e saving throws looked like for an ogre. But let me ballpark it at 20% chance to pass (similar to the 3e numbers quoted).
So the real chance to one shot is: .7206 * .80 = 0.57648 = 57.65% chance. Aka yes a 6th level caster could scorch those ogres in a single fireball, but its close to a coin flip that it may take 2.
3e: Our goal is to get to similar chance to our 2e numbers (aka 57.65% to one shot with a fireball).
Since we are still using that same 80% success rate, we need ~72.06% to oneshot the ogre. That is found at 9d6 (horray) at 71.81%.
So total chance to one-shot with that fireball is 57.48%.
Ok, these numbers agree with the quoted post. Its 6th level in 2e vs 9th level in 3e to get a ~57% chance to one-shot an ogre with a fireball)