I think there is some confusion between a couple things. A sort of "input lag" and actual rate of pitch.
Sure in a conventional cable pulley flight control system airplane, a larger aircraft might have a slower rate of pitch for the same control deflection. However aircraft designers can augment this in different ways with larger tail surfaces, control surface deflections, etc. If they weren't able to do so, you could imagine a 747 that has manual and hydraulic controls would be nearly impossible to control compared to maybe a 737-700. The difference in aircraft size is so great that with that argument you'd expect a 747 to be uncontrollable in comparison. However in the real world if you compare, they are both able to attain similar 2-3 deg per second of pitch on rotation with little delay and with a relatively similar yoke movement.
Even with conventional controls that design is indeed possible. With FBW the possibilities are endless. As you say yourself, the A320 family flies similar because of the FBW. An A318 and an A321 tend to feel the same no? Well as far as I know that isn't actually 100% the case but I think that goes beyond the scope of the simulation.
Now what I think this user is talking about is not the rate at which the airplane can change pitch, but the response from the controls. If he makes a control deflection, there is a gap in time until the aircraft actually responds to the movement. The rate at which the airplane actually pitches up could be as fast or slow as you like. However if you go full aft on the stick at VR and the nose doesn't lift until beyond V2, that could be a problem. Now I wonder how this would look from an external view. Is it a case of the elevator itself responding slowly, or does it go full up and then there is some delay until the aircraft actually pitches?