I think people can affect history. And, those changes can be large from the perspective of the people living in or near those times. But, we're talking the grand course of human history. And, no, I don't think individuals bear much on that. Smaller history, on the scale of a century, sure. Longer than that, the effect of individuals diminishes greatly and continues to diminish with longer time scales.
Mr Awe
I would disagree that the impact of individuals diminishes over time, if anything the potential is for it to increase.
I get what you're saying with your peasant example but I'd disagree with that. Again from the grand scheme of things, sure, the specifics would change. You'd have a different cast of characters but the story would remain largely the same. So, we'd end up with a 20th Century, different individuals in the population in some cases, but essentially the same plot.
But, here's an interesting point. Ok, so Adelaide dying was a fixed point. But, that creates many, many other fixed points. Nothing could happen so as to prevent Adelaide from being born and living in such away as to get her to the base. Also, nothing could happen that could change the timeline for developing that base at that time (The DR said the fixed event was on that day at that time.). So, that casts a wide net for any time change that could prevent that fixed event from happening. Nothing could kill one of her ancestors before creating their progeny. Nothing could kill anyone crucial to the base, etc. So, this specific fixed even implies oodles of other fixed events that are necessary to produce it.
But, obviously no one knows because we can't change time.
Mr Awe