The aim wasn't just to subtract- sometimes things are more "yes and".  You raised some good points and I agree that there are some parallels between Sam and Rey, while I also see significant distinctions in how their respective arcs were set up as well as how Sid was positioned in the story vs Luke to where I think it's not 1 to 1 if you're comparing franchises. Dewey was Han though, absolutely.  And both deaths were equally hated by the fans, haha.
But my thing is I always thought it was beyond obvious that Stu was coming back since the first trailers for 5, and I thought there were actually some neat thematic and fun meta commentary things you could do with that, beyond just fun of having a returning Ghostface. I've always had my cards on the table here about being a basic b**** Stu truther, eating up every clue.  Which is why I always felt things were gonna culminate with a Sid and her family/Stu story, because there's no real reason to bring back a legacy killer without going all the way full circle.  I would've of course wanted to see how the sisters' story continued and intersected with that, but having followed the franchise closely for a long time and knowing Guy Busick's stance on it, I've long suspected we were always building towards some version of a Sid/Stu confrontation, especially if he had any say in the matter.  Of course it's tough to say what would've been had Neve been in 6 and Melissa/Jenna had been in 7.  It's all speculation, but I think the evidence is strong.
My biggest fear with this movie is that I'll get what I wished for and regret it, because I truly believe there could be a good version of that despite the people who hate the idea on principle.  But having to write out main characters is a very tough pill to swallow, the reasons for it are even tougher to swallow and there's an unfortunate stink on this movie.  I do feel it will be lesser than it could've been because of that, even if it's still not bad on its own and I am a fan of many of the people involved creatively.  So it all leaves me feeling a strange mix of hope, excitement and dread.  A feeling I haven't felt for a franchise film, ironically since the leadup to each of the Star Wars sequels!