I can agree to that . . .
to a certain extent.
I play DMC4 at a fairly high skill level compared to most people. So I'm quite used to the core mechanics of DMC4 as well as the advanced gameplay. If you don't believe me, here are some videos of me playing as Nero and Dante.
I'm the Nero player in this video. The Dante player is my friend named 2bepower.
Anyway, you're partially right. Sure you need to be more experienced with the combat system compared to the casual player in order to make statements such as "this game is clunkier" or "this game is slower" as critiquing the game. But you don't need to be a
complete master of combat system to say such a thing. You only need to dive deep enough to fully understand the core concepts of it. (Like Jump Cancelling, Buffering attacks, Weapon Switching, and non repetitive combos executing combos)
After working with DmC, I can safely say that it's actually less responsive and more inconsistent with buffering inputs compared to the previous DMC games. It presents a major problem when you're trying to do technical things with the game. Especially if certain inputs won't register just because you're inputting too many moves all at once. (which I never really had much of a problem in DMC4 when playing as Dante).