I probably wouldn't call myself a Halo "fan," but I will say that I've thoroughly enjoyed playing through the game with a splitscreen friend in the past, and Halo 5 removing the feature for what feels like very arbitrary reasons (you can totally just lower the framerate for splitscreen; Mario Kart does that and it's totally fine) does annoy me. Halo's gameplay and story have never really been enough to engage me, and I find myself only really getting into things when I've got someone by me to talk/make jokes/team up with or just shoot in the back when they're not looking.
I don't think Halo 5 automatically becomes a bad game without it, but it does remove any incentive I had to get the game somewhere down the road. Without a friend, Halo's campaigns are ones I find generally pretty boring to play, so yeah.