The argument that non-FFB wheels have some advantage is based on older gen sims. It's an anachronism based on older and poorer FFB. With rF2 (I'm not sure about other current sims- rF2 is the only current-gen sim I play) the FFB is much more advanced than older sims and gives you real and pertinent information you need to race fast and consistent. With flat spots, once you have one, it's not the vibration that's the prob, it's working around that bad tire and the FFB gives you information about what that tire is doing. The real problem is that the flat spotted tire will keep locking up into certain corners. I was in a race with the Spark F3 at Putnam a few weeks ago and I cooked the RF tire- flatspotted it on lap 13 (I remember the corner and the immediate vibration and the OH S#!% when I realized what I had done... while in the lead!) By the FFB I was getting I was able to drive around the problem and still win. Without the FFB there's no way I could have known right away I had a flat spot, that there were certain corners where I had to baby that RF tire and just how much braking to use.
FFB being faster or not is totally subjective. Some people in our league don't run any and they are quick. Don't know if they'll be quicker with it, only they'll know if they try it.