I see Birkenstocks as orthopedic shoes that shouldn't be worn on a healthy foot. Think what happens if you push a brick in an arch from below. Huaraches, Luna sandals etc. are a better option healthwise, people run ultramarathons in them and the design has thousands of years of history.
I am apparently ergonomically blessed in that despite running up to ultra marathon distances, I rarely get injured. Nothing unusual about my feet, average size 10 foot with a normal arch, average pronation. I’ve worn Birkies for thirty years without complaint.
And people will run ultras in/on anything. I would not be shocked to find out someone ran Western States 100 (miles) in a pair of Birkies.
