I’m not going to spoil the ending of the game, nor what’s shown in the video above, but you need to watch all 18 minutes of the video above if you’ve played and beaten Metal Gear Solid 5 and felt the same way I did: confused and disappointed in the story.
Episode 51 shows what would almost definitely have been the actual ending to the game, were it completed. The big question lies in why Hideo Kojima’s swan song with the series was released as it was without what appears to be the actual ending. This is Metal Gear Solid - the ending is of the utmost importance.
Whether due to time or budget constraints, the game will always be as it stands now: ultimately unfinished. Kojima is no longer with Konami, and creating what’s shown in Episode 51 authentically just isn’t within Konami’s capabilities. At least we have this glimpse into what could have been.