Basically each core of the FX CPU is really weak but when all cores are working together it is better than an i7 3770k. You can see this advantage in things like video editing and other programs that use multiple cores properly.
Games are not like that and still rely heavily on what one core can do. I'm not saying that games only use one core, but you can't split a process onto two cores which is why if a CPU has better single core performance it will generally be better for games.
If I remember right, the way the FX series work is that each core shares resources with another, so Core 0 and Core 1 both share cache and such. Some people say they are technically not real cores or whatever. But they work best for multi-threaded programs.
The way an older 4 core i7 works is that it has 4 real cores and hyperthreading. Hyperthreading is basically what Intel does to get double the threads, they do this by having each core virtualise two cores so your OS sees 8 threads instead of 4. This is not as fast as 8 real cores but in some situations it can be much better than 4 real cores.
You can never directly compare different processor architecture to each other as there are many things that make them completely different. Clock speed and core count isn't everything.
edit - maybe I make small error in some of this, it's been a few years since I was really into hardware but it should be mostly correct