The fuck do they need 7 years for? Last gen you could develop two games in that timespan.
New IP, new setting, new engine (in the case of Horizon), etc. Horizon didn't actually need 7, but it spent some time in the 'concept oven' while most of the devs were still working on the previous title. As far as 'Ghost Sushi' goes, it sounds like the environment is finished, the gameplay is still being worked on, and who knows how much of the story has been nailed down aside from the core concept. 2019 sounds plausible IMO, especially with Sucker Punch working with Japan Studios.