Your calculations likely don’t account for immunity gained.
Re-opening some things is not a contradiction, as long as you keep the reproduction number <1 you are on a path so that you can contain things. Stricter measures mean you hit them earlier, laxer measures means later but you might not damage the economy as much ... but in any case they said if it flares up again the strict measures come back.
That said permant economic damage will be due to politcial policy choices not due to a two-three month lock down. Consequence of protecting the rentier class instead of businesses and people.