When I think of Cliff's character, the expression "Imitation is the sincerest form of flattery" comes to mind. I understand completely what you're saying, midwest, but I think Cliff did evolve, only not in a positive way. He started out as a fairly likable (IMO), mostly decent person with scruples, who wanted to help people by going into politics. When JR derailed his political career, it unleashed a side of Cliff's personality that kept evolving more and more into a JR-like character, but without the smarts or the charm. He was smart in certain ways - he became very successful in business, at least in part because he was so driven to one-up JR. But you're right - he never learned. He kept trying to beat JR at his own game but could never get the upper hand. The more he tried, the more scheming and dirty dealing he did, the more he seemed like a copy-cat JR. He made it his life's work to avenge the wrongs that Jock Ewing had supposedly done to Digger, and in the process he became just as selfish, manipulative and underhanded as JR.
I always felt sorry for Cliff because he was short-sighted, as you said, so we knew JR was going to destroy him, but he never saw it coming. Several of the female characters told him he was becoming just like JR, in particular Afton, Mandy, and his own sister, Pamela. I remember Katherine telling him he was a petty little man. But he never listened and he never learned. I always wished he would settle down with Afton - she was so crazy about him - or later on with Liz, but his obsession with JR pretty much precluded him from having a real relationship with a partner.
I also felt sorry for him because I think he took it much harder than Pam when their mother left them (he was older and understood more). That had to leave an indelible scar; maybe he thought he was unlovable and subconsciously sabotaged every relationship he was in. Once in a while we had glimpses of the old Cliff when he showed a softer side to his sister and his mother, and later with little Christopher, but these were few and far between. Pam even warned her mother about his greed and ambition. Still, I found him to be a pretty sad, although interesting character - sympathetic in the beginning, but later - not so much.