Few die of normal flu, because many are immune. And if no people are immune, then more will die. Covid-19 is no different than Spanish flu.
You seem to agree that they are totally different, except that "no people were immune". Even if that were the case (it is not), that still makes them different
This is like saying that a fast car and a slow car are exactly the same, except that the fast car has stuff inside it that makes it go faster. Total non argument.