Having followed sports my entire life, and played a bit... Lebron is not a good example. He is a freakishly transcendent talent, the exception to the rule.

There is no "right time, right place" factor for Lebron, unless we're simply considering the fact that he lucky enough to be born at a time on Earth when professional basketball is a thing that exists.

    Would his career have worked out if Carmelo was drafted 
    to Cleveland and Lebron went to the Nuggets? What about 
    if Lebron needed to do a year in college now? How would 
    that have impacted his trajectory?

Assuming his work ethic and will to succeed aren't somehow impacted there is literally no permutation of events, no alternate universe, in which Lebron James does not become the NBA's greatest talent for roughly a decade. He is/was that good.

Generally though, I do agree with you.

Lebron's championships, as opposed to his individual performance, are definitely somewhat the products of circumstance. He heroically dragged some mediocre supporting casts to the Finals and fell short a few times, which simultaneously proved both his own brilliance and the inability of even the arguably-greatest player of all time to do it all on his own.

A lot of supremely talented athletes have failed to find success in professional sports due to simply never finding a good fit for themselves where they were able to shine.

Similarly, there have been some oddballs who have found great success thanks to being in circumstances in which they were able niche for themselves. James Harden is a modern NBA player who comes to mind. The Rockets play a somewhat bizzarro style that caters to Harden's bizzarro skirting-the-rules game.