We didn't really shut SARS down so much as it seemed to have shut itself down, conventional epidemic control measures were enough to contain it and it was not quite easily transmissible enough to sustain itself in the wider population without being allowed to gain a real foothold undetected first.
That last point would be why you would not expect (and I would think it is impossible) to find that at the end of the day COVID-19 will be anywhere near as deadly as SARS. We have strong evidence that it takes truly extraordinary measures to suppress this new virus at a rate that will in fact eliminate it from a population when compared to SARS. SARS simply didn't spread that widely because if it did that would directly contradict the relative ease of its containment.
Likewise influenza was well known before the 1917 pandemic, or H1N1.. and?
https://www.nature.com/articles/d41586-020-02598-6
"Evidence from people infected with other coronaviruses suggests that the damage will linger for some. A study published in February recorded long-term lung harm from SARS, which is caused by SARS-CoV-1. Between 2003 and 2018, Peixun Zhang at Peking University People’s Hospital in Beijing and his colleagues tracked the health of 71 people who had been hospitalized with SARS. Even after 15 years, 4.6% still had visible lesions on their lungs, and 38% had reduced diffusion capacity, meaning that their lungs were poor at transferring oxygen into the blood and removing carbon dioxide from it."
We know this much and SARS is poorly studied because it faded away so we generally lost interest in it. This virus is both similar and different enough to be very, very wide spread so even minor negative effects over the total population that gets moderate to mild cases will have the potential to have very large impacts on worldwide health.
As time goes on we are going to better document the consequences of mild and moderate cases and understand these things better, caution seems advisable until we do.