Just do it right back at them :3
In all seriousness though, the best way (for me personally) to counter these players was Fleet Foot itself. I started with it at a very low level and just practiced with it A LOT until I could eventually take most players in a head-up situation.
The other potential counter I'd recommend is Cloaked (probably the #1 Slot One booster in this game). The fact that it takes away both the player arrow and all noise that your character makes allows you to get the jump on people and catch them off-guard, and therefore kill them before they can abuse that ROF on you. I'd use it if it suits your playstyle more and/or you don't like Fleet Foot.
Also, stay away from ROF. Not only is it generally considered scrubby, but it also decreases the M9's long range capabilities.
Just learn to strafe FF + ROF really doesn't give one the upper hand all you need to do try to strafe & avoid as many bullets as you can, ROF burns through a clip in no time in a tense situation 99% of the times they will try to reload while still aiming, you kill them then xD.
AK has great stopping power / heavier bullets but you must make sure all your shots connect because of the slower ROF.