If half a dozen kids with a botnet were able to take down PSN and xbox live for days, then a hundred or more determined overwatch cheaters with botnets can all but incinerate blizzard's network infrastructure.
I don't condone it, I'm just saying, don't expect this to work in the first couple of weeks at all.
But here's still hoping that these kids either don't follow through or that blizz finds a way to mitigate it.