Also, from what I've heard people put 0 WAYYYY way above 5, and 6 and just barely below 3. With people saying Billy Coen ruined the game for them in a lot of ways.
That's the first I've heard that. Billy was awesome. He was the original RE badass before Chris started punching boulders or Leon became John Wick. I've been hoping for his return for some time.
Also, CV isn't just a spin off. It was the original RE3 and a direct sequel to RE1 and 2. It moves the story forward more than most of the mainline entries. RE3 was originally actually the spin off and all it really does is tie up Racoon City. Otherwise it didn't really move the story forward. IMO CV should definitely be included with the mainline REs.
Most people I've heard is that he's too snarky and flirtatious, generally unlikable and doesn't fit the RE franchise too well, they also cited hating his character design.