...and then their best writers were moved around too much and CW stupidly tried to have their whole team of writers handle 5 different shows with 12-24 episode seasons(Arrow, Flash, Legends, Supergirl, and Black Lightning) all releasing around the same time for crossovers. The best writers being moved around was the biggest issue because you'd randomly have a season of one of the 5 shows that would suddenly skyrocket in writing quality and then immediately dip the next season.
Supergirl Season 4(The Lex Luthor season) was direct proof of this. Season 4 was written almost as great as a season of the 90s Justice League Cartoon show, with a great ending and epilogue and it's one of the best seasons CW ever managed to put out during Arrowverse run, along with Arrow Seasons 1 and 2, Black Lightning Season 2, Flash Season 1, and Arrow Season 5(Prometheus season). It was especially jarring for Supergirl because the quality of that show's writing was in the gutter since season 1, and then suddenly became good in season 4, then it quickly fell right back into that gutter a few episodes into season 5. It was almost like the writers were saying 'look how good we could make things if we had less episodes and more resources/time'.