Yeah, I agree. The idea is just plain dumb, but maybe with better execution I could have accepted it. It was a poorly constructed mystery to the point it isn't earned. What's overlooked about these movies is that they're constructed as mysteries, and great ones at that. I'd say they're as much as whodunits as they are horror.
When Roman unmasks himself in front of Sidney she should have said "Who?" Sidney has never met this person before. What made all the other killers effective was the fact Sidney knew them in some way or another. Sidney had no interaction with any of the characters/suspects besides Kincaid and Emily. Dewey's line in Scream 2 about the killer already being in her life sums it up. That's what makes Ghostface so scary. One of these people are pretending and the drama is how much Sydney can live her life with this knowledge.
I really wish they went with Williamson's original idea for 3. That would have been amazing.
Just have a strong motivation with strong execution. 1,2, and 4 all accomplished this.
For the record, the Jill stuff was brilliant. An inverse of the original? The supposed new Sydney that takes over the franchise being the killer to have her own franchise? ****ing brilliant. That's the type of ideas and understanding I hope these new people have.