To be really honest, a high damage roll could wipe more than that. After realizing that and, as @
Mistwell pointed to us, that this spell is supposed to wipe armies, not single opponents, I have to agree that it's probably fair as it is now.
No, I never compared. If you look at my view of character power you'll see that I believe comparing different classes is bad for the game, as each one should do its thing. But someone else said that fighters and rogues would have to witness the destructive power of the mage, and with that I disagree, because each of those classes is equally - or even more - destructive.
"Well, but the rogue needs to succeed in various ability checks to be destructive as a mage".
And that's probably the reason why they designed a rogue that will need a lot of effort to fail an ability check in his fields of expertise. In gameplay, the fact that a rogue needs some rolls to accomplish this great feat of strength is neutralized by the fact that by level 17 he won't achieve anything below a 25 in a stealth check. That means a non-proficient creature with Wis 20 will only spot him with a 20. No, I won't pick the bestiary and count how many of those creatures have Wis 20.
So, by the RAW, it's easy as it gets for a rogue to enter a heavily guarded fortress and kill a 94 HP opponent, unless you're going for a theme park-style game, where suddenly the kings that a level 17 rogue needs to kill become level 18 paladins with level 16 bodyguards. While I believe there's a lot of space for this kind of game (I play a lot of WoW, the quintessential theme park adventure), that's not how I like my D&D. I like it when level 17 characters don't see a lot above them in the food chain.
Cheers,