I think op is confused about the meaning of one hit wonder.
Aespa has arguably the largest dedicated fanbase of any kpop girl group after blackpink. Their album sales keep increasing year on year and their music is well received by their fans.
I personally love their music and each subsequent release ends up outdoing the prior in terms of my Spotify streaming stats. So no there hasn’t been a decline for people who actually like their stuff. Girls and spicy are both great title tracks. Better things is one of the least boring English songs to come out of a kpop group recently.