If Horizon got a sequel, Days Gone should have got too.
Both are very similar - mediocre story, good 3rd person combat, large open world with beautiful vistas, checklist style missions, all crafted with high production values. I think it's the theme, horizon is more accessible whereas Days Gone is gory and more lite horror that will make first time gamers not pick it up.
Personally I think out of all good zombie games out, Days Gone is the weakest. Exceptional 3rd person combat? TLOU2 Exceptional movement, parkour? Dying Light 2 ( and 1 ). Fun, cool melee first person combat? Dead Island 2 Tight, Horror, gameplay, puzzles and atmosphere? RE4R. More horror? RE2R. Horror and story? Silent Hill 2 Remake.