Disclaimer 1: Nothing I am about to say is a comment on the girls talents but JYPs mismanagement. You can be talented and pretty all you want but if your company doesn't know what to do with you tough luck.
Disclaimer 2: For the sake of simplicity I am counting Itzy in 4th gen even though some people consider them 3.5 gen.
JYP truly is lost. When Twice was at the same point in their career that Itzy and Nmixx are now they were pulling all kill after all kill. Even when BP came they both appealed to different demographics so Twice didn't have as much competition. In the sense that BP was girl crush appealing to the west and Twice was bubblegum pop appealing to the Asian market. So they were both on top in their respective genres. But with Itzy and Nmixx neither of them have that. Their competition is a lot more fiercer. Aespa, Gidle, Lee Sserafim, NewJeans, IVE are all killing it. If they weren't from JYP Itzy and Nmixx (provided they were mismanaged the same way) would be B list at best.
Itzy started off strong but somewhere they lost it. I wanna say after Sneakers is where they started going down, I personally didn't like the song but I heard it did well in SK and I can see why. Boys like you was the worst (those lyrics are a crime) and the rest were just meh. Bet on me was good and Cake was okay but nothing really memorable. Cake just sounds like it can be any other girl groups song. I feel bad because looking at their documentary you could tell they are stressed, they are at the point where they are suffering an identity crisis. You can make different music while still having the same style. Spicy and better things still sound like Aepsa songs despite not exactly being the Kwangya concept.
Nmixx has been trying to make up for their debut ever since.. well...their debut. The last CB was off. I listened to the songs several times and can't even remember a word. Plus having a member leave like that has got have been a hard blow. No matter the circumstance loosing a member is hard on a group. Nmixx has an identity but JYP just can't give them good music. He is still stuck in his Suzy trauma and refuses to individually promote the girls even though in 4th gen you kind of need to do that.
I just feel for both groups because they clearly know their situation, JYP is breathing down their necks, competition is fiercer than ever and they're just stuck. Nmixx more so because they're still so new. I think JYP just needs to get a new team for both groups, just fire everyone, get a new team. With Itzy they should just go back to their roots and stick with that. With Nmixx decide either change the concept or find people who can make good songs for their concept.