I think you missed a huge portion of hunters here. Myself I use folding blades if I can get them. I do have a fixed blade boning knife which I use as needed, but it's my folding knife that is the most important. I've never owned, but have tried the replaceable blades. I'm not impressed with them in the slightest. They are knives though, no reason they wont work. Blades are pretty thin, basically box cutter blades, but at least the replacements are reasonably priced.
When you get in certain areas where you want to keep heads, whether for trophy or CWD, having a way to cut them off is a great thing. I just don't see a replaceable blade knife cutting a head off. There is some finesse involved, but you kind of have to just go for it once most of the ligaments are cut. You can carry a second knife, or saw or whatever. I've seen people on this site argue over ounces. Well here's an easy way to save ounces, just bring one single good knife that does everything, maybe not great, but does it all with minimal problems.
I see lots of talk about carrying sharpeners, and I just don't see why anyone would. There's all kinds steels out there, some sharpen easy, some don't rust, some stay sharp longer, etc. Any good steel will hold a plenty good edge for at least an animal, and honestly I'd be pretty disappointed in a knife that was dull after 2 animals. We aren't talking about butchering, only gutting and quartering animals. I think a sharpener is a great thing to have in the truck, but I would never carry one with me.
My preference for knives has never really changed over the years. I've always preferred a folder with a blade 3"-4" long. I don't think I've ever tried a 5" blade folder, I can't think of one. Locking type doesn't make a huge difference to me. My work knife is a liner lock, and my hunting knife is a back lock. I've tried fixed blades, but that's more bulk on your side. I've tried pocket clips, keeping them in the back pack, and even on a necklace. For me it is a no brainer, a leather belt sheath is the only way to go. My all time favorite knife is a Buck 110. There are lots of folders out there that can work as good. I like my brass and wood, and the 110 is such a rock solid design with minimal places for crud to get trapped in. It really is a fixed blade that folds. The icing on the cake is a drop point blade on them. The classic clip point is fine, I just like a drop point a little better, seems to be easier to guide over the guts without poking the stomach. People can argue about 420HC steel all they want. The way Buck makes their blades is great. They aren't hard to sharpen, and you wont need to re-sharpen them until you are done. I have not had any rust.