People can always argue about whether something was inevitable, in the air, etc.
Point is ... there was nothing in terms of a game that was played. And then there was OD&D. Absent Arneson's original idea (which, of course, had antecedents) and Gygax's adaptation, expansion, and commercialization, we wouldn't have what we have.
Or, put another way-
Two economists are walking down the street, and they come across a $20 bill.
The younger economist says, "Hey, look, it's twenty dollars!"
The older economist shakes his head at the younger economist, and scoffingly replies, "That's nonsense. If there was a twenty-dollar bill in the middle of the street, someone would have already picked it up by now."
Now, I am not entirely sure that history is the same as the efficient market hypothesis, but I do know that at the end of the say ... it was first.
Sorry, I assumed it was obvious.