That's preposterous. Hood/Heyward's "strength" is to control gaps (i.e. 3-4 scheme). That's not to say that they wouldn't prefer a gap-shooting scheme that would free them up. That's not the point though. In such a scheme (I'm presuming), DL playing more freely means LBs who run around less freely (due to taking on more blockers). It's a trade-off.
Now... getting back to Hood/Heyward. Yes, they would make more plays that way. But they aren't suddenly going to turn into Warren Sapp/Chris Doleman because of such a switch. Hood/Heyward are limited players, which suits them to 3-4 schemes. It's not like DL's system is making "great" players subjegate themselves.
The fact that neither has done much to distinguish themselves is more a commentary on their talent than it is the scheme. They're both ham & eggers.
Very well said. I do think that Heyward has a bit more upside than Ziggy Hood, but ultimately, there is a reason that these guys were available where they were in the draft.