I've always heard a lot of people "get" the flu but it's asymptomatic or virtually so. My experience suggests this is true. In a household of five I was the only one who got the flu (the first time I have in about five years) and felt truly sick for several days. We are all in constant close contact. Three of my family got slight symptoms of the same illness at the same time or within days but didn't develop fully. Likely all five of us are now immune to that, including ds who developed no illness at all. So really only one of us got sick but we all got immunity--I'd bet that at the least the four people who had some symptoms fought it off for sure.
It doesn't require a commitment to suffer again and again and again every year to acquire immunity without vax. Howevre, we do not get to control the process like we think we are doing when we get shots.
My flu vulnerability seems to be in the neighborhood of the 5 years pattern for my entire life. I've never had a flu shot. Apparently the same pattern, approximately, applies to all of my children. It's actually unusual for there to be more than a cold or two in any given year in our household.