In real life: the current Metal Gear team is separated from their leader who they dedicated themselves to, some for almost two full decades, and is seen as a nearly messiah figure to others in their field. Now they're on a deadline to create a game against all odds using already made assets or risk being replaced by Konami and either fired or forced to work on whatever else the company wants.
The game is about: A team separated from their leader who they dedicated themselves to, some for almost a full decade, and is seen as nearly a messiah figure in their field. Now they're forced to survive against all odds using scrap and other materials found to make weapons to fight off being killed or transformed by an unknown infection that makes mindless zombie-like creatures do whatever it wants.
If these Mother Base soldiers are the same ones (the Wandering Mother Base Soldiers side op) you extract in Metal Gear Solid V: The Phantom Pain, no wonder they're so messed up in that game. Spending an unknown length of time in a desert dimension filled with zombies can't be good for your mental state.
There are some subtle foreshadowing elements which show that Goodluck and the Captain have a deeper relationship then he's letting on. Why does he spend so much time looking over the coffins for a candidate? Because he hasn't found a corpse that looks like the Captain yet. Why does he have tapes that are pertinent to the group's interests, even after he's arrested by Section? Because he lived through that experience with them and knows what to warn them about ahead of time. Why does he obsess over calling the player character Captain and having everyone else call him that? Because when he was Chris, that's what his little boy self remembers everyone calling the player character.
Why did Chris take the code name "Goodluck?" They're the last words he heard from everybody as he went through the wormhole.
Early in the game as you first time see the Base Camp, you see a ruined Mother Base with Diamond Dogs logo on it. Keep in mind that Diamond Dogs didn't existed yet at the time of XOF attack and it might be just written as lazy asset reusing or designer error... Until The Stinger, as explained in the main page, where it's said that the wormhole above Mother Base during XOF attack didn't appear, possibly due to Stable Time Loop preventing the appearance of the wormhole in the first place.
The secret message "KJP FOREVER" can be interpreted as an "up yours" to Konami for firing Hideo Kojima and steering the franchise into a downward spiral of ruin.