Yes, it's as crazy as it looks. Once you get up onto the trail about 30% in, crowds thin out because most day trippers are just going for selfies around the lake or to the first viewpoint they can get. They have started doing timed cable car tickets now to try to work on the crowds, but no matter what it's going to be very crowded.
It is a beautiful lake, but it's been ruined by social media and overtourism in many ways. The crowds got so bad that the lovely family who runs the inn up there decided to shut down because it got too crazy. We stayed up at the lake in the inn the summer before they closed a couple years ago for a week and really enjoyed it, but that's because we got to be there before and after the day trippers arrive.
They're also dealing with the very imminent danger of a major landslide. The side of the mountain has been falling apart for years now so one side of the lake is completely closed. When we were there we could hear rock slides in the middle of the night and the town of Kandersteg has been doing a bunch of work below Oeschinensee trying to make sure that when the mountain does give way that it doesn't destroy the town.
I don't like to make great uncrowded spots too obvious on public forums to ruin them the way Oeschinensee has been, but since you're a skilled hiker beyond the normal day tripper, you can private message me if you want and I can tell you about a couple good alternatives that aren't crowded that I don't share on public forums.