Snark aside, we have massively more people alive today than in 1900 and yet the proportion of people that die in armed conflicts is— while horrific- barely noteworthy in most years around the dawn of the 20th century and not infrequently dwarfed by the body counts racked up in those days.

That's true if your definition of 'die in armed conflicts' is limited to 'the soldiers on the battlefield.' If you extend that definition a little to 'people who would not have died if there hadn't been an armed conflict' then you need to scale it up to about a million people a year today. That's just from 5 countries where it's been studied. Globally it's likely to be much more. There's some good information about it, from a credible source, here: https://costsofwar.watson.brown.edu/costs/human

you also need to compare people injured so badly that they are significantly worse off for life after the war is over, as most of those people would probably have been killed in previous wars but thanks to modern medicine can be kept alive to suffer for years afterwards.

not a knock on modern medicine, and probably the people who survive are happy that they did for the most part, however if you compare the results in the way you did, you should compare those as well.