I find my own hatchlings are much tougher than store bought chicks if you go on a chick by chick basis.
In other words, the store ones are often tough because they made it though shipping and all the weak ones, the ones who died in shipping, and the culls from the hatchery are never seen so you see the "top" of the bunch. However, they are more prone to pasty butt and some death due to residual shipping stress.
The ones I hatch at home are usually pasty butt and death free. I don't like to assist in hatches because I personally think if the chick is gong to make it, it is going to make it. Of my hatched, I have had to cull three to spraddle leg caused by a bad incubation, and that is pretty much it. The dozens of other birds have made it just fine.
I say the majority of chick death is due to shipping stress and getting chilled.