The stats I've seen seem to indicate that COVID has behaved (in terms of waning) more seasonally than in response to lockdowns.
For example Sweden, who didn't have lockdowns anything like what we've seen in other countries, have a curve[1] that tapered off too. At deaths per capita, they're lower than UK, Spain, Italy, Belgium, and many more.
Which is not difficult because you picked the worst of the worst to compare them with. Compare them with other nordic countries like Norway or especially Finland and Sweden suddenly looks like a complete failure.
Most curves look a lot like an explosion that burns out locally too fast to sustain a continuous fire. This could lead to some kind of seasonal dynamics without external factors.
One exception is maybe Argentina. Since the beginning it was more like a continuous burning fire - until they stopped. What did they do?
You can see normal flu seasons and the out-of-season huge spike. Then you can see subsequent bumps on a per-country basis. Some countries had multiple spikes and lockdowns etc.
These charts tell exactly the story I'm telling. The peaks and troughs appear at the same time for countries with strict lockdowns as for those with less strict / non-existent lockdowns.
This isn't going to correlate to one thing. The seasonal impact is real, but that doesn't mean lockdowns don't work.
You would also expect to get no (average) excess mortality for the year if you just killed off the frail earlier than normal. This is not the case, excess mortality just returned to normal levels. You would need either a spike in the other direction or a step change down to fit with your theory.
You can track the yearly excess mortality data here for a few countries.
https://www.economist.com/graphic-detail/2020/07/15/tracking...
Keep an eye out.