To me Supergirl and Brainiac were awful too. Brainiac omitted the dramatic subplot with the Kents from the original story that gave the story it's emotional core and elevated it above your run of the mill superhero slugfest. The Girl from Krypton was a mediocre comicbook to begin with (don't even get me started on Turner's art....rest in peace tho) so no I wasn't really surprised about the quality o the cartoon.
But I think JL: W was worst than Man of Steel (came out right after it and I actually made my peace with MoS since then...but not with BvS).
IMHO the only animated movie that managed to balance the darker tone with watchability was Gods and Monsters. I really liked that one.