It is indeed a guessing game for influenza vaccines as the prevalence of each genera and type of flu virus  varies throughout the year whilst their mutations/antigenic drifts also give rise to new strains. This highlights the beauty of the mRNA approach as it can be used to generate a protein antigen common to all the influenza variants (early dev days for that though). But I agree, if you’re young, healthy, know that you have no underlying conditions and your immune system is strong and there is clear prior understanding of the action mechanism of the virus (which is not always clear if the virus is novel) then arguably no need for a vaccination (although anyone can develop pneumonia). The anti-vax game changes if/when a novel virus evolves/mutates into one that spreads both easily with a very low survival rate across all age groups. Not beyond the realms of possibility and indeed may be one reason for species extinctions in the past.