AaronOfBarbaria
Adventurer
The majority of times someone says there is something off about the 5th edition CR system, it is as a result of them expecting it to do something other than it's intended function (it's a rough benchmark of when a monster probably won't kill anyone in the party before it dies, not a benchmark of what level of party the monster will push to their limits and nearly triumph against), the DM playing the monster in a way that makes it a push-over, or a combination of the two... and throw in a side of analyzing CR not based on the chances that something goes one way or the other, but on how things played out that one time with how the dice rolled, completely ignoring how unlikely it is that what happened that one time to happen at all.
This doesn't seem any different, since a solar is actually very unlikely to be severely affected by any spell (decent AC, lots of high ability scores in the saves it isn't proficient with, more proficient saves than most monsters, and magic resistance on top of that) let alone be completely defeated by a single spell. I'm not saying it didn't happen, just that it happening was a statistical outlier and thus isn't evidence against the CR system working as intended.
This doesn't seem any different, since a solar is actually very unlikely to be severely affected by any spell (decent AC, lots of high ability scores in the saves it isn't proficient with, more proficient saves than most monsters, and magic resistance on top of that) let alone be completely defeated by a single spell. I'm not saying it didn't happen, just that it happening was a statistical outlier and thus isn't evidence against the CR system working as intended.