I can confirm this, 100%. With HD/D, and 18x20's in general, you need to keep racket head speed up, way up, in order to generate the requisite lift and spin. If your strokes get too slow, you shorten your follow-through, lose spacing, or do anything else at sub-optimal levels, your game will absolutely suffer more than it will with a 16x19. In other words, the ceiling is higher but the floor is lower.
In my personal experience with the 97D, it's a very similar situation as with the VCore 95 -- you need to pretty much be full gas at all times, non-optional (the difference versus the VC95 though is that the D has a way more consistent string bed and much higher overall stability, so at least all that effort is going into producing a more predictable outcome, on average). That said, the moment where things start going south is usually in set number 2 or 3 where I tire, even just a bit, then get lazy on a stroke or two, and inevitably I'll either dump a ball into the net because I didn't go out of my way to aggressively brush up/around for enough lift, or send a ball long because I left the face too open and didn't come over the top enough -- and I know in both instances, it's usually due to fatigue, not just a random blip in technique. All-in-all, though, I love the 97D, but it definitely requires full commitment to the cause at all times.
One final point: I'm not normally one to gate-keep racquets based on level, but in this case, as with the HD, I would agree with others in saying that unless you're a 4.5 at minimum, but more than likely a 5.0, and at least not that far off from your physical prime, you're probably better off with either a lighter or less-dense frame (or both). I know that may seem dismissive, but for those who haven't played the D/HD for at least 50 hours, do so, and I think you'll come to a similar conclusion.