It's hard to say if it's interesting or concerning, but an aspect I've noticed is there's no real mid tier in regards to 4th Gen Girl Groups.
Either you're top of the mountain or barely getting by. It's a real haves and have nots situation.
Previous gens there were groups that could chart well, but couldn't sell or sold great but charted poorly and a lot that charted decent and also just sold decent (relatively speaking). But nowadays it feels like either you're top of the charts and selling gang busters, or you can't see the top 100 and struggle to even do 50k.
Now there are two exceptions. Fromis 9 who sells decent and charts decent and Loona who at least sells decent but two groups doesn't really make a mid tier. It feels like a lot of these groups haven't landed as strongly as they should have.