If you think about it, despite not having big fandoms, many 2nd gen ggs even from smaller companies charted well. They had some fame in Korea which lead to cf and drama roles.
4th gen ggs are just killing it in all metrics
But for 3rd gen, aside from big 3 groups very few ggs shot to fame and even then it was short lived. Gfriend, MMM and OMG managed to chart well, however not even at the same time. MMM rised after gfriend momentum cooled down and by the time OMG was charting, MMM charting cooled down.
So in a single year, very few 3rd gen ggs were succeeding compare to 2nd and 4th gen.