Historians have challenged at least one of the assumptions you make in your post.

John Unruh, The Plains Across, is still considered the definitive work on traversing the Oregon Trail. Revisiting older attempts at calculating mortality rates, he estimates a survival rate of 96%, so mortality at 4% overall.

More recently, a group of scholars at BYU has focused more closely on Mormon records, since that allows for comparison between pioneers and those who stayed put/once they were settled in the West. They calculated a 3.5% mortality rate for pioneers during travel and within one year of arrival in the west (often California), paired with a 2.5-3% mortality rate for people who did not travel.

So the chances of dying as a pioneer were slightly higher, due to new risks like snakebite (this could be a factor elsewhere, of course, but pioneer diaries mention it so it seems to have been at least seen as an elevated risk) and, tragically, children being crushed to death by wagon wheels. But overall, you could die of dysentary by staying put just as easily as on the Oregon Trail.