You also have to account for the issue that the first round of people getting Aids in the US and europe were largely part of the gay population at a time of extreme homophobia compounded by fear of this unknown disease. So - many were denied medical care or given extremely insufficient medical care, and the minimal treatments we had were delayed even further. Ie - if someone had the exact same disease today, without using any additional scientific breakthroughs or treatments from the last 50 years, just by not ostracizing the patient, you would see significantly better outcomes.

Then, there is the flip side that people would hide they had the disease as long as they could. Once they couldn't anymore, it was near the end - giving the impression of a sudden death after starting symptoms.