In my experience, the worst agents (psychopaths and narcissists who will fuck up the company for their own gain) are almost never job hoppers. Sociopaths understand social power and how to get it, and they know that it takes time. They don't job hop often (and they look before the leap) because they rarely need to, being inherently good at politics and quite capable of getting a pay/promotion trajectory far better than would be available to them if they changed companies (and had to start over, politically speaking) every few months.
The worst corporate sociopath I've ever seen is 28 and has just been named CEO of a company with about $10 million in revenue. He's been there for 4 years, and it's his second job since college. The company will probably crash and burn under his rule.