We had data from December 2019 until April 2020 showing that it spread quickly and can kill you.
We also had data that strong action can stop an outbreak (i.e. Aviation flu, Swine Flu, Ebola, etc). Sure when we took those actions early enough to curtail the outbreak it leads to people thinking the actions were useless (see Y2K debate) but it doesn't actually mean the actions were useless. People only notice when the dam collapses, not when it doesn't.
By March 2020 we had the Diamond Princess Data which established an upper bound of 1% case fatality rate (CFR) for COVID. We already knew then that it's definitely not the Spanish Flu (2.5 - 10% CFR), not Cholera (3%), not Smallpox (3%), not SARS (11%), not even Measles (1%-3%).
Not only did we never do anything like COVID measures for any of the diseases you mentioned but the WHO described the individual NPIs that would later make up the COVID "lockdowns" as "never recommended under any circumstances" in their 2019 flu pandemic recommendations.
What happened with COVID was an unprecedented overreaction by historical standards where we threw overboard everything we knew to try authoritarian gobbledygook on the back of the carefully cultivated FUD around COVID coming out of China.
We also had data that strong action can stop an outbreak (i.e. Aviation flu, Swine Flu, Ebola, etc). Sure when we took those actions early enough to curtail the outbreak it leads to people thinking the actions were useless (see Y2K debate) but it doesn't actually mean the actions were useless. People only notice when the dam collapses, not when it doesn't.