You're not wrong about anecdata. But there's a less callous way to respond to someone who just explained that two of their relatives are dead or seriously ill...

"Interviews were conducted 14–21 days after the test date. [...] Among 292 respondents, 94% (274) reported experiencing one or more symptoms at the time of testing; 35% of these symptomatic respondents reported not having returned to their usual state of health by the date of the interview (median = 16 days from testing date), including 26% among those aged 18–34 years, 32% among those aged 35–49 years, and 47% among those aged ≥50 years. Among respondents reporting cough, fatigue, or shortness of breath at the time of testing, 43%, 35%, and 29%, respectively, continued to experience these symptoms at the time of the interview. These findings indicate that COVID-19 can result in prolonged illness even among persons with milder outpatient illness, including young adults."

> Uncomplicated influenza signs and symptoms typically resolve after 3-7 days for the majority of people, although cough and malaise can persist for >2 weeks, especially in elderly people and those with chronic lung disease.

https://www.cdc.gov/flu/professionals/acip/clinical.htm

Seems like over 14 days of flu symptoms is common.

Precisely what overall percentage of flu patients across the general population experience continuing symptoms after 14-21 days?

(Any common influenza in any typical year in the past decade is fine.)

(However, regardless, I do not consider researching your line of reasoning to be a valuable use of the time I have available for this discussion, so I will not be doing so. It’s not personal at all, though I imagine that’s of no comfort. Perhaps someone else will do so; I see someone trying in another branch.)

While your math is sound, your empathy is horrendous.

How about, "I'm so sorry about your loss. But it doesn't change the fact that..."