Armies of chickens today would be something like ARM server chips, which have been touted for a long time but have perpetually stalled out precisely because replacing one powerful core with a dozen weak cores doesn't work. Even for commodity tasks, but especially when you throw the need for interconnect scalability into the mix.

Don't make the mistake of thinking that a large system is implicitly using weaker processors. They're as powerful as we can make them, some tasks just need a lot of them.