No they are not bad for gaming. i have an fx-6300 with a radeon 7850 2gb and i get 60fps BF4 ultra, 60fps skyrim ultra with 2k/4k textures, 40-50fps in crysis 3, 60fps tomb raider ultra and so on. They are nice and cheap too!. Th give you an idea on cpu performance: games become more cpu bound when you lower the graphical settings down to minimum, and i can get 160-180fps in bf4 on low.....so the fx is very capable for a budget cpu.
The i5 will be better at single or dual threaded games as it has higher single core performance, but most games these days are optimized for multi-core. Put it this way running bf4 on ultra (minus AA) pop a clean 60fps with 35-45% CPU usage. They are more than capable of gaming very well. For example on the intel side, skyrim runs a little better on my i5 (i5 2500 thogh) than the fx,but in all respects both are capable of all games on the market today.