> (wear masks, be vaccinated, test yourself before and after the event, etc.)
^^^^^^^^^^^^^
> The result was that precautions were largely ignored by everyone at the event.
You don't know if the attendees were vaccinated. You don't know if/how they tested. When I got vaccinated, and also when there wasn't a wave, I got more lax. It requires focus and attention span to follow the precautions. Except for vaccination. That's a shot, perhaps some side effects, and you're good to go for a while. Masks have more adverse side effects. And I say that as someone who has a needle phobia, got vaccinated multiple times, but also who wears glasses and prefers the fresh air over the mask (nausea).
I've also done self-tests which, in start turned out nothing, and then once it onset (I already felt ill) suddenly bingo.
> My personal take from this was a) FFP2 masks work
> I strictly wore one indoors and didn't get sick
N=1
Masks primary role is to ensure you don't spread COVID, not that you don't contract it.
The more plausible explanations that you don't got COVID is that you were a) lucky b) vaccinated c) used more precautions like social distancing / didn't frolic around the crazy 'social' people who YOLO.
With masks it requires cooperation in order for it to work. It doesn't work like a condom: put one on, be protected. Everyone puts one on (a good one, as you asserted, though even a mediocre one is 'Good Enough') and then the chance it gets spread is minimal.