The question you raise,
@Kenny Coyote, about how much our career changes us is really profound. It can change us slowly and subtly, in ways we may not even realize.
Most of us choose our professions when we are in our twenties or even younger. We are making this decision for a lot of reasons, but experience is rarely one of them. We can also get so caught up in doing our jobs that self-reflection is not something for which we always have the time or energy.
Regarding JR, he seemed to be born into the Ewing Oil life. I'm sure doing anyhing else was never on the radar for him, and his relationship with Jock made his destiny at Ewing Oil seem a fait accompli.
Would very young JR be appalled if he saw his future and some of the things he would be doing?
One of the reasons Dallas became such a phenomenon is the layers in the characters, both seen and unseen. Your question about JR is intriguing because it's ultimately about fate and how much control we have over who we become. If Jock had blatantly favored JR over Bobby, would Bobby have become the ruthless, scheming one?
Your question makes me see the Jock, Bobby, JR dynamic as similar to the Willy, Biff, Happy relationship in The Death of a Salesman. Another reason Dallas was so popular. It touches on the human condition in a similar manner as great plays like DOS.