I don't think the G in MAGA is harking back to the founding of America or the settlement of the continent, more like the 20th century, when America was the world's superpower, it was wealthy and influential, it's made a lot of goods, its population was relatively wealthy and its entry into both the First and Second World Wars meant that it and its allies won those wars.
A lot of older Americans remember when America and Americans were the envy of the world, when there were jobs for all, when a lot of working class people lived in nice homes in nice suburbs, because the man could get a well-paid blue-collar job that supported his whole family. That era, the 1940s and 1950s, is when Trump was growing up - he remembers those times and I think that's what he wants to try and recreate. America in that era was certainly the envy of much of Europe, which was struggling to get back on its feet after the Second World War, its cities ravaged by bombs, its economies shattered.
But look at America now - it's not the envy of the world any more. It's riven by culture wars and urban decay, its manufacturing and industrial heartland is now called The Rustbelt, it has a disaffected and angry underclass made up of the kind of people who once worked in those factories and mines and mills. The downtown areas of many of America's great cities are full of homeless people who are either drug addicted and/or suffering with mental health problems. It's really not the utopia it once was.