https://www.theguardian.com/world/2021/nov/23/pandemic-hits-...
Keep in mind, this isn't just 20% fewer people to deal with COVID, it's 20% fewer people to deal with, well, everything, for years to come. I'm sure someone's done the calculations on what the consequences of a decimated healthcare system are, if you want to go look for them.
How much worse do you think everything you've listed would be if we had started with 20% fewer healthcare personnel? Well, guess what. That's how bad it will be from now on, because we couldn't all cooperate to take measures to ensure the healthcare system didn't get overwhelmed in the first place, and doesn't continue to get overwhelmed.
That's why I asked how you could arrive at the converse conclusion that lockdowns are net beneficial for mental health.
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[0]: https://www.beckershospitalreview.com/workforce/about-1-in-5...
[1]: https://medicine.yale.edu/news-article/burnout-alcohol-ptsd-...