Those brands have the most powerful servers in the shoe game for their websites and the fact that they split the releases geographically helps a lot to prevent from crashing situations (except when it comes to yeezys).
Adidas have no app such SNKRS, just one to secure pairs before the release day if i'm right. Even if, Currently, it seems hard to beat SNKRS on the comfort of the copping experience, at least when there is a decent amount of stock.
Cart jack horror stories happen everyday mate
but if you ATC fast enough on Adidas the pair will be secured the time you checkout normally. But be fast