I don't know if the bolded is necessarily true. While diseases are heterogenous, the response to them is remarkably similar. Like the differences are so small, they are probably irrelevant. There was some interesting studies starting back in the late 1990s, early 2000s when RNA profiling and proteomic analysis were just cutting edge. These studies were under the umbrella NIH program called the Glue Grant. It was essentially trying to see if the heterogenous types of critical illness had genomic/proteomic signatures that could clearly be delineated and that could potentially lead to personalized medicine for critical illness. It was interesting because globally, the project failed relatively speaking, enough so that the NIH cancelled the project after a decade or so. I mean it generated a lot of data, but all that data essentially said was that if you get shot, lit on fire, go through a windshield, have the flu or get necrotizing fasciitis, your body's response (ie the RNA profiles) are like ~90% the same. In fact, even to this day with array profiles looking at thousands of genes, you can still find lots of papers looking for single candidate "biomarkers", which is just another way of saying a vast majority of the human body's response to stress and critical illness is the exact same... so much so that we can't tell the difference.
The reason I mention that is that one of the CAP/ARDS studies excluded influenza because of data with worse outcomes in steroids. Yet, for some reason, it works for COVID and sepsis and aspiration and EVALI, etc. etc. When you think about it and put it in the context of the data that shows the body doesn't care, it's all inflamed, you 1) start to question the validity of the hypothesis that influenza is different just because and 2) realize that steroids are used so commonly because to some degree in inflammatory critical illness, the hammer of steroids makes at least a little sense since all the body does is generate a whole bunch of non-specific nails. Now, what is different is timing and duration of onset. If you been hospitalized for X,Y,Z and then you get pneumonia, you're immune system is in a much different state then if you get pneumonia walking in off the street. That's where every single ICU study, ever, has failed to discriminate.