I followed Smallville religiously from Ep1 to the very end, and I still don't understand the incessant complaints that we didn't see him either as Superman or doing more Superman-like things during the course of the last few seasons.
The show was never about Superman. It was about the teenage (and subsequent twenty-something) Clark Kent, and the trials, tribulations, mistakes and discoveries that he went through which eventually enable him to become the Superman we know and love. The moment he became Superman, Smallville fulfilled its brief and the show (almost literally) ended as it had achieved its purpose. Tom Welling understood that and stated as such in many interviews; he even alluded to the fact that pre-2001, when he was only just auditioning for the show, the fact that it was about Clark and not Superman made it more appealing to him. No-one ever promised that we would see Tom playing a fully fledged Superman in the show, be it for a short or long period of time - but what we got was pretty close in terms of character by the time we'd made it to Season 10. People came up with their own expectations of what the show was about and when they weren't met, there was a misjudged sense of being cheated.
I think a major part of the problem is that Tom Welling was physically such a good fit for the role that people found it hard not to envisage him in the suit. When Superman Returns was released in 2006 as Smallville was hitting season 6, Tom didn't really look that much younger or physically inferior to Brandon Routh despite the fact that one was playing a 20yr old Clark Kent and the other playing a 30-something Superman/Clark. Both were 6"2/6"3, well built, perfect facial features for Superman, etc. There was a sense that if he looks so much like Superman, why not go the whole hog? Yet to do so would have meant sacrificing the story which Smallville was trying to tell and it would have become another Superman series.
By contrast, Gotham - which is currently airing - takes a similar premise to Smallville and shows the evolution of a young Bruce Wayne. Yet because he's still only around 13 or so, there's no expectation that we're going to see him fully suited up as Batman anytime soon.