Also, remember that after Shavuos there were a good few weeks of packed regular weddings with no spike following that (just to throw in a wrench).
The most annoying argument in all of Covid. Nobody ever claimed
every gathering will spread Covid. The problem is when covid is spreading, gatherings exacerbate it
Yomim Tovim in shul are not that different than weddings
They are very different because they are a constant bubble. At least 60% of the people in a shul are there regularly and not in any other large gathering other than immediate family. So if everybody in Shul gets covid, it's much more likely to stay contained. People are also going to be more aware about it.
A wedding is 50 people from each of those shuls. If everybody at the wedding gets it, it's going into 50 different shuls. And if everybody in a shul gets it, it's going into 50 different weddings.
Obviously, nothing here is absolute, but the increased odds make a big difference over the long term.