I dont know, the more I think about it, the more I think I agree with this
Crisis Gives Tom Welling's Clark Kent the Farewell He Deserves
That would be true if somehow, somewhere, somewhen, we, as the audience, knew, Clark Kent/Superman would have defeated every villain in the gallery.
Clearly, that was not the case. Lex Luthor is the President. The one who will have the blood of millions (according to Hourglass s01e06).
Clark gave up his powers in a time when Lex is president, his arch-enemy, in a position of power. That's not the perfect send off, far from it.
They tried to do a sort "whatever happened to the man of tomorrow?" thing but in that case, all the villains were defeated. Superman was no longer needed.
Not the case with Smallville.
This is just bad writing.
We all know this is a arrowverse storyline but at least, they could respect the smallville legacy as they eloquently put it.
They trash it just for the sake of nostalgia and trying to rise tv audiences when their shows clearly fail to do so.