Yes, I have been doing that with the modulation wheel for literally hundreds of patches so far. Often, I have 8 filters assigned to the modulation wheel for formant like effects. Needless to say, its a little tedious and time consuming to do so, not to mention, if the all tab's filter is somehow altered by mistake, would negate the formant effect since it would link all layers to the 'global' filter. I personally think a master layer that would adjust each individual layer relatively could greatly increase Dune 2's creative flexibility! Does anyone else agree?
Rapid for instance is also very similar to Dune 2's 8 layer architecture and has a master filter that is assigned relatively and it is really awesome. First thing that came to mind would be how great if dune 2 also behaved this way. I think both linked and relative absolutely have there usefulness