I don't see a dissonance that can't be overcome. All those things can be survived, after all, or not.
I mean, the dissonance is pretty blatant to me.
Imaro is making two points. First, that it is conceptually unsatisfying that a powerful and resilient adventurer, who has endured dragon's breath and mummy rot and the manipulations of devils and the caprice of fey nobility and (etc., etc., etc.), could die of a completely mundane illness in the span of (presumably) only a few days. This is an incongruity, because the character has clearly survived, even
thrived, under far, far greater danger with no meaningful side effects. It's not like we're talking about a person IRL who won wars and survived amputations
in their youth only to die of the flu at age 65. This is a character generally in the prime of their life and who has proven herself far superior to much more dangerous threats. Even from a naturalistic logic perspective, there's reason to find this dubious.
And, secondly, an argument I know you are likely to dismiss out of hand, but which really does matter quite a lot for many people: the fact that it is an unsatisfying
played experience—an unsatisfying "narrative", if you will—to lose one's powerful, heroic character to something so insultingly
banal as a slightly worse than usual head cold.
Just as it would be unsatisfying for the true perpetrator of a grisly murder to be a random stranger who just happened to be walking by,
even if such a perpetrator is more "realistic" than one of the named, participating characters in a mystery, because the point of engaging with a mystery as entertainment is being able to
solve the mystery yourself, at least in principle. Just as it infamously was unsatisfying and deeply unpopular for the
Game of Thrones TV show to trash all or nearly all of the arcs that characters had been building to, merely for the shock factor of doing something unexpected but (at least theoretically...) naturalistic, like Danaerys suddenly descending into madness or Jaime Lannister abandoning the people he's made sacrifices to help because Cersei wooed him back. Just as it would be unsatisfying for, say, a show or movie or book about racing to feature a race where the POV character is disqualified before the race even begins due to a technicality and just...leave it there, even though that is a real thing that certainly happens to a lot of people IRL.
Something being grounded and naturalistic for the everyday lives of completely ordinary human beings on this island Earth is, unfortunately, not at all a guarantee that the experience of playing through such events would be a good one.