Can only add my anecdotal info too.
Purchased a few batches of various breeds of chicks from an OH hatchery. We always picked them up as day olds and drove them home ourselves, and they were never shipped. Chicks placed on puppy pee pads then onto shavings (in a wood brooder box) so really good footing and no splay issues in any of these birds.
This spring we got 28 chicks across 10 breeds (straight run) from a hatchery in another state. These chicks were all placed in a single chick box (no dividers, but with the usual excelsior padding), and shipped Express to us. They arrived at our PO 18 hours after the originating PO got them. Two had mild cases of splay legs and I wonder if the constant movement and shuffling of the box while being shipped and transferred caused the splay legs in these fragile chicks or if they would have had it anyway. We used a rubberband/straw contraption for 2 days and they were all better after that.
Lastly, I've seen it mentioned numerous times that hen nutrition can impact the health of the hatching chicks, with leg issues being impacted by nutritional deficiencies.
Good Luck!