When its good, its good. And when its bad, it's really bad. DOA 5's Online is really bad if you notice dropped inputs, hitching or stuttering and otherwise unplayable elements. Lacking those things, the online functions well, without a feeling of input delay.
Thanks to your statement, I can totally see players smashing their faces into their buttons, and like you I've had trouble punishing that. I haven't had the time or chance to go into training mode and run through frames to see whether Kasumi's (or others) PPP...xN are truly unsafe on block. At best they might be -7 which still makes them safe, but throw punishable. I think that frame data might be lying at least a little, though.
I have punished stupid stuff from other players online. Although I've had trouble using counters from block to do it, since the way the inputs work now is that you have to let go of block and then tap it and the appropriate direction at the same time and many times I screw up on that.