When the 3rd and 4th generations are still going strong (although thankfully Bibi ended the possibility of the last remaining 2nd Generation singer jumping into the arena), the wall is too thick for the 4.5th gen.
Out of the 4.5th gen, only Illit has gone somewhere, and its new comebacks were weak.
Babymonster got good views thanks to Southeast Asia but otherwise it is weak, and Meovv was a bit less impressive. Don't really hear too much about Izna,
and now HeartstoHearts and Kiiikiii have jumped into the arena.
So 6 acts in the same arena.
Around 2014-15, several newer gen girl groups debuted. I am not counting Mamamoo since it had a different fanbase.
Red Velvet and Lovelyz debuted from SM(at that time Woolim was part of SM), Twice from JYP, CLC from Cube, Sonamoo from TS(still had some power back then), April from DSP(which still had some power remaining back then), D-IA from Kwangsoo's company (which also had some power remaining), 7 which I could remember immediately.
Out of these, only the two acts from major companies, Red Velvet and Twice, plus GFriend, so nugu that no one really counted them in, went anywhere. The rest didn't really go anywhere, including Lovelyz who fell way, way short of what GFriend did with very limited resources.
Now the acts for the 4.5th Gen are better supported. Illit (belieflab - Hybe), H2H (SM) and Babymonster(YG) are from major company, Meovv is well connected, IZNA is an audition act, and Kiikii is from Starship, which has some punch because of IVE's successes.
Personally, it will be an overkill. Only 2 or 3 of these will survive, and Illit already has an advantage since it did have a sizeable hit while the others did not. GFriend's earlier successes kept them in the top rung for quite a long time despite of basically being abandoned after Hybe bought its ex owner out, and no one is going to buy out Belieflab now.
With Illit already taking one of the 2 or 3 spots, the remaining 5 acts will be fighting for at most 1 or 2 spots.
KPop is in decline and the halcyon days are over. Too much of a good thing actually kills interest. Out of the remaining, I do think that H2H, being an SM act, will have the greatest advantage.