Wordpress running on Apache with mpm-prefork - which is the default out the box - does insane bullshit that can indeed cripple the whole system. I run Wordpress via fcgid with mpm-worker by preference, because that way it's isolated in its own little sandbox to crap all over. Funnily enough, you have to run it that way in nginx too.
tl;dr the claim that Apache was the problem is Marketing Bullshit.
From what I recall, Debian currently defaults to threaded unless you install mod_php, in which case it insists you change to prefork because PHP still isn't threadsafe.
tl;dr the claim that Apache was the problem is Marketing Bullshit.