I'm not saying I think any number is correct, but if I may, here are 3 rebuttals to your point:
- Those figures are for 1 encounter. If you go to the shops, or to a commuter station, or a big workplace, it doesn't take long to meet 1000 people. The pandemic is taking place over months, not 1 day.
- If you let people stand a metre closer you'll get more than twice as many in the same space. So again, more encounters, more transmission.
- We're pretty "flexible" with these rules. Currently, lots of people let the spacing slip to around 1m, either for convenience, or accidentally, wotever; at least with the "TWO METRES!" message, these encounters are minimised; if we go to a "ONE METRE" rule that will become the average, with lots of people standing closer when it suits them.
Obviously I have an opinion here, or I wouldn't bother posting! My current gut feel is that 2m should stay as the default, apart from VERY limited scenarios.