There are too many factors to consider imo, but I think two important ones are the differences in population density and overall population.

Today we live closer with our neighbors than any time in history, not to mention a majority of the population are now packed into cities. This was not as common in 1918, and certainly not on the same scale in terms of numbers. Not to mention supermarkets were not as convenient as supermarkets today so people were generally more self-sufficient. So transmission rates were certainly lower in 1918.

If I had to guess, if the Spanish flu hit a major city(specifically India or China) there is no doubt death totals will exceed the 1918 ones simply because hospitals will get overwhelemed within days of the outbreak.