^Well, the problem with Smallville was that its creators probably never expected it to run more than 5-6 seasons, so as it kept getting renewed over and over again, they had to stretch it out and bring in more and more elements from the comics and from Clark's adult life, thus bringing it closer and closer to being an actual Superman series -- but they still insisted on maintaining the original conceit of being about Clark's life before he became Superman, so it got increasingly labored. I and plenty of other people felt that they should've just renamed it Metropolis and made it a straight-up Superman show, a sequel to Smallville rather than just more seasons thereof, but there was too much resistance from within. (I have the impression that Welling refused to wear the tights, which is reinforced by the fact that we never got a full shot of him in costume even in the series finale.)
The creators of Smallville had no clue what they were doing and only enough story for 2-3 seasons, at best. Thankfully they left the show and it became a lot better with more comic references in it.
They should have continued it and just made it a Justice League show. But I guess Arrow is doing great on it's own and the JL movie, so it would be over kill.