The observed mortality rate already accounts for advances in medicine that are actively being used, no? Mortality rates are easy to compare: x% died back then and y% die now. Those numbers take into account the various characteristics of the disease and health care.

People aren't saying this acts like the 1918 disease so it should have the same mortality rate. People are saying the observed mortality rate is the same. That's in spite of medical advances.

You’re making a lot of assumptions. Sure, if the reported death rate is correct (it isn’t; it’s going to end up much lower), and the medical system in Wuhan is up to first-world standards (it isn’t; they’ve had to scramble to build halfway adequate infrastructure for the population), and the distribution of victims is the same as the 1918 flu (it isn’t; this virus kills mainly old, sick people), then sure, you can just compare mortality rates.

But since none of those things are true, you can’t. It’s not like these parameters are fixed; they’re dramatically affected by the time and context in which they’re measured.

They're hardly useless, and if the current virus is killing the same percentage of people as the 1918 flu despite all of our medical advances, that's a strong indicator the current virus is significantly more potent, which makes the blithe assertion that "the mortality rates aren't all that high" even more dubious.