I'm not so sure this is true.

Here in the UK the deaths are climbing back up again as the second wave comes in. Yesterday we had 241 Covid-19 fatalities, a number not seen since the start of June.

Additionally, the way the UK is counting deaths changed a few months ago. Originally we were counting everyone that had been diagnosed with Covid, now if the death doesn't occur within 28 days of infection the death isn't counted as a Covid-19 death.

And finally, we're testing a hell of a lot more now so the alleged case numbers back in April (~5000 a day) don't marry up at all with case numbers now (~20,000 a day). I'm guessing back in April it was closer to 80,000 cases a day in reality, which would make the disease just as deadly now as it was back then.