All opinion and all subjective, but I loved the show's fourth season. And FWIW, I'm hardly alone: It won that year's Saturn Award for best superhero TV series, beating out all the other CW DC shows as well as comicbook series on other networks, and Melissa Benoist recently called it her favorite season of the show. Kreisberg wasn't missed at all.While S4 of SuperGirl was good for what it is (it was "Alright" in the grand scheme of things, but something about the writing & characterization still went wrong), but S5 & S6 wasn't as stellar IMO as earlier seasons.
I dunno, something went horribly wrong after S3 of SuperGirl, I lost interest after S4.
S5/6 was a slog that I couldn't be bothered to finish.
So it's literally sitting on my "Unfinished Pile" of things to watch.
I agree that the show's quality absolutely fell off a cliff with season five, however, for reasons I've never been able to figure out.