I've only been in early December and it was busy (as is standard for TDR), but not crazy busy.
We missed the launch of the Christmas decor and merchandise which are typically very busy days.
That typed, we just got back from a trip to Tokyo and we visited DisneySea on a "low" crowd weekday and it was still insane! It took a very long time to even enter the park, despite arriving early, and wait times ballooned enormously once everyone was inside. In the first ... five hours, we only did one ride (40 minute wait), met a couple of roaming characters, saw a show and ate lunch.
It wasn't until the last hour or two that the park actually seemed manageable. So, I think DisneySea's new "normal", even with reportedly "low" crowds, is just so busy that it can almost be unenjoyable.
To be fair, a lot of the high capacity and ... "filler" rides weren't operating - Indiana Jones, Sindbad, 20,000 Leagues, Aquatopia, etc.