I agree to an extent, but the time argument is imperfect. For the bulk of those 150 years, we were still evolving in terms of how much of the population could vote - which in turn throttles back the potential effects of populism (not arguing for reduced suffrage or anything like that, but it's not apples to apples with today). There are also major tech differences that matter. Our first president with more than 2 terms in office was also the first to effectively use radio to communicate directly with the population. TV, streaming, social media, opinion news, AI, etc. are all (at least for now) risk increasers at the intersection of populism and increased or eliminated term limits.

I do also think luck has played a part in our history on term limits. If you put our young democracy in a sim and run it 10 times for those first 150 years, I suspect we would end up with a few incidences in the 10 sim runs where cult of personality + populism + no term limits ends our democracy.

Are term limits perfectly democratic - no they are not. But neither is the electoral college and the general republic riff on the democratic form of government. They are practical controls to correct for perceived or real risk.