I have gotten a flu vaccine every year since I was 18. The worst flu I ever had was in January 2020. (I was tested and positive for influenza)
Fever for 4 days, horrible coughing, vomiting, barely able to get out of bed. Flu vaccines certainly provide some cross-immunity when the vax isn't matched to the strain, but not too much. That's what my doctor told me when I complained to her (when she told me I had tested positive for flu) that I'd gotten the annual flu vaccine the preceding October. Depending on the strain vs the vaccine for that year and how big of a mismatch it is, it can really whip your ass despite the vaccine. That being said, the flu shot is a good idea for anyone, and crucial for seniors.
This is why it has a vaccine. That prevents it, prevent seriousness of symptoms, and deaths. (yet a large percent of the population doesn't get it, and so 50k us citizens die each year)