It's quite a shock to me. This group is directly managed by Bang Si Hyuk, and that alone will give them such a huge boost. Lessera girlies have a more mature sound and concept, along with a huge, loyal fanbase since debut. This consistently sell the best in K-pop (look at the concepts of the most top-selling girl groups now). Groups with a concept like Newjeans (especially with chills, slow tempo songs) usually don't do that great. I don’t even know what their concept actually, it's not cute concept either like Twice or even Stayc. Their songs are just too chill, while K-pop songs, especially the TT, are usually more upbeat and energetic. Twice songs for example even with their cute concept, they have very cheerful songs. I don’t know how to explain it, but I guess you all understand.
I never thought that Nj would outsell Lsf, especially with Sakura's huge fanbase in Japan and China. Chaewon is also very popular in Korea and Japan. I have checked their album sales and all them are all selling more than 1 million already. This is such an interesting twist. I know Lsf faced a huge scandal during their debut, but Antifragile proved that it didn't affect them much. I can even say that they are generally the most liked 4th gen girl group now. K-pop stans seem to adore this group, especially Eunchae and Yunjin, compared to their peers.
This is not to criticize Nj. It's just me who never thought that concepts and especially songs like theirs would become very popular in K-pop. It's something usual for soloists but not a K-pop group. But good for them, they already managed to get song like Ditto (idk if it is a ballad or not but it is a slow tempo song) a PAK and topping the charts while usually only BB and soloists are able to do so. With this, I can see they will easily matured their songs later in their careers.