No it is not. One of the main advantages of Apple is that you get at least 5 years of update support.
Having to buy a new phone just to run the new OS sounds like Android hell.
I love having the latest and greatest when the beta 2 of iOS hits months in advance.
My iPhone X is still running iOS 13 like a champ. And my 7 Plus ran iOS 12 well too. I skipped the XS generation and held onto my X and 7 Plus realizing that those two phones combined were better than one XS, and I sold my 7 Plus to help fund the 11 Pro Max.
I’d happily keep this combination for the next year. Starting with the 7 series, I feel like Apple finally started making iPhones with longevity in mind. I feel really bad for all the people who still have 6 and 6S’s though. Those phones were so flawed!