The black death was in the 1300s, when the average life expectancy was in the mid 30s. The mortality rate was so high because the mortality rate of everything was high. If you got the plague you would die. If you got the flu you would die. If you got cholera, tuberculosis, or diarrhea you would die. If you got just about any disease you would die.
The black death killed millions of people in Europe. Most of the rest of the world was unaffected. The 1918 flu was the first truly global pandemic. Millions of people died in every continent on Earth, roughly 5% of the world’s population at the time.
Spanish flu maybe killed as many people as the black death, but was not as catastrophic, as you point out, given the lower population in the 1300s.
What would you know about the rest of the world back then, given that they couldn’t read or write?
The Black Plague recurred many times over the centuries. In fact it was also the plague that hit earlier in one of the later Roman eras, I think Justinian.
But just because any disease was dangerous to get back in the Medieval era, does not mean the disease does not pack a punch.
The death rate of BP is STILLL a mammoth 11%, TREATED. Untreated is like 30%! This is a very dangerous Plague.
Meanwhile, let’s double the apparent rate of COVID. Nope, doesn’t compare.
The BP killed at least 30% of the POPULATION, never mind those infected. It was no slouch compared to this scamdemic.