Look, I'm a fan of Welling and Smallville and have watched the show from the first episode. He seems a great guy in real life and I love his take on the Clark Kent/Blur character.
And I'm also a Superman fan, and have enjoyed ALL the movies.
But let's not kid ourselves. Snyder has said Cavill was his first choice, and Manganiello his second. There is absolutely no evidence to suggest that Welling is still 'WB/DC's first choice for playing Superman'. If they wanted Welling bad enough, they would have got him, one way or another. There was nothing to suggest he was even in the running for this movie. And after this Superman movie is released, there is virtually no chance they're going to muddy the waters and go with yet another actor if they decide to have Superman appear in a Justice League movie - in all likelihood, it will be Cavill.
Welling has played the character for 10 years and done it great justice on TV, and that time is coming to an end now - he was just never meant to do it on film. Move on people.