That is not what has happened in the past. No it is not true that everyone had symptoms within the same 2 weeks. It has become very clear that it was floating through the community long before then. Probably by close to 2months.
I believe as things stand, it doesn't have the potential for a serious outbreak anywhere near the level we saw. Given the number of variables that will slow the spread including the fact that people know to quarantine if they were exposed/have symptoms (no one quarantines when they have the flu), many people are immune, less contact with people, at risk people still taking extra precautions, and I'm sure there are others I missed. We also know more about it now and we know what to look out for, and we have testing available to identify an outbreak way earlier instead of attributing it to the flu. I had a colleague who flew to CA before purim, a few days after he came back he wasn't feeling well so he either went to or called a local urgentcare, he asked them if he should be worried it may corona and they laughed at him, if that happened now he would immediately be sent for a COVID test.