While I would say that he doesn’t get as much as we all would like, I wouldn’t say he completely gets sidelined. I mean, one of the best parts of the show and what I most remember, at least for me, were all of the cute and funny interactions and jabs between him and Lois and the rest of the Daily Planet crew. Like this one, one of my favorites:
But, I see what you’re saying. You’re talking about how they neglect to explore Clark Kent as a character and his development as much as they do with Superman, and on that, I don’t disagree.
I mean, to give credence to your point, there is literally an episode called “The Late Mr. Kent” where he has to fake his death as Clark Kent from an attempt on his life with a car bomb for investigating a corrupt detective and is forced to just be Superman for a time, much to his frustration. They literally “kill off” one of the main characters to make room for and give more screen time to the title character.
Granted, it’s the main conceit of the episode, and it is executed wonderfully, but they don’t ever really have any episodes dedicated just to Clark Kent, save for when he’s a teenager in the second episode and that Legion of Superheroes later on. Lois gets some. Hell, Jimmy gets an episode.