Transition point or not, it was a wargame. Period.

And to top it all, why call it a RPG element if it was introduced in a wargame?

It is a wargame element.

It is not about agreeing with or not.

When a plate has no food in it, getting people to agree there is food in it wont fill up the belly. It is another round of magical thinking.

XCOM is not a RPG, people agree with that or not.

And the question was about finding the influence of RPG onto it.

Another point: campaign existed in wargaming before the 1970s. Campaigning is what induces the requirement for units to turn from rookies into veterans.