One of the reasons Supergirl struggled all season is because they failed to juggle far more plot lines than they could handle. And this all came to a head in the finale, because despite all of these plot lines basically none of them paid off.
Jeremiah Danvers and Cadmus? No payoff there. We haven’t seen him since he fought with Hank Henshaw and the only time anyone seems to remember him is in the face of Lillian Luthor.
Speaking of Lillian Luthor? What about the whole Cadmus story line? Not resolved; she still runs Cadmus and it’ll likely still be a problem. But what about her and Lena? Okay, so they worked together to make the lead thing. But we don’t see them at all beyond this. Lena still doesn’t like her (rightfully so) and Lillian really didn’t cause any problems so nothing really came out of them in this finale.
But what about Lena? Like I said, there really was no payoff with her mother. No payoff with Rhea because they didn’t interact all episode. And her friendship with Kara/Supergirl didn’t really have a payoff either. They barely interact in the episode. You can’t even say that it paid off because she made Supergirl that remote. Because A) That could’ve just as easily been Winn’s doing and B) That seemed to more so come from a place of distrusting her mother.
So what about Winn? He helps, but does he really have his own plot? No. His biggest plot all season was Lyra and even though she got a mention this episode, she has been MIA for several.
Well, what about James? If you think James has had any sort of payoff all season, I could laugh at you. He was almost entirely absent from the finale. He’s barely been present for a plot all season to even have a payoff. The whole Guardian plot? I honestly don’t understand at this point. At the beginning, this was a big thing he really wanted to do. But these last few episodes it seems like they’re almost trying to undo this whole plot.
What about J’onn? Honestly, his story arc this season with M’gann might actually be the only one with a payoff. He’s happy to see her again, and he is not at all put off by the white martians she brings to help.
Cat Grant? Honestly, her return was one of the biggest things carrying these last two episodes. Her return was great and helpful to the plot, but because she has been gone it’s not like we’ve been following an arc of hers all season, waiting to see a payoff with her.
Alex? Alex had almost no impact in the finale. Honestly, had she not been in it nothing would’ve changed. And what about her big arcs this season? Her dad and Cadmus? All we got out of that was her distrust of Lillian Luthor which really didn’t affect anything. And Sanvers? They should have left it at “I hope so”. Sure that would’ve been a little disappointing for shippers but Alex’s proposal takes away from her whole arc this season with Maggie. Alex was really learning to grow into herself through this relationship and now it just feels disjointed with a rushed proposal that really doesn’t even make sense. They just said “I love you” like two episodes ago where not much time has passed.
But the lack of payoff that pisses me off the most has to do with Mon-El and Kara. And this really has nothing to do with shipping.
Do you like Mon-El? Then you should probably be pissed that they gave you so much of him all season only to take him away. Don’t like Mon-El? Even if you’re happy he’s gone, you should still be pissed that they spent so much time on him this season for him to wind up completely gone anyway.
So with him now gone, that begs the question of whether or not the entire Daxam plot had any payoff and the answer is no. With them being off of Earth for good, they won’t directly affect the show going forward.
As for indirectly? Mon-El is arguably the only Daxamite that had any impact on every other character, but I don’t think anyone expects Alex or James or Winn to be affected by him being gone.
The only person he was ever intended to impact was Kara. And for what? The purpose of breaking her? People may argue that he developed through Kara all season. But Kara didn’t develop through him all season and guess what? She’s the goddamn protagonist and he’s gone now anyway. So her lack of development all season really shines now.
The scene where Mon-El leaves is all about how “no matter where he ends up he’ll be better because of her”.
And I think that sums up the season pretty well. It’s all about him, not Kara. You can argue that he didn’t grow at all anyway, and really almost none of the characters have. And even if all of that were true, he’s gone anyway so it doesn’t matter. Just like how pretty much every plot of this season doesn’t matter because none of them paid off in anyway.