Perhaps some company politics and a history with that particular captain?
Not sure but just because one pilot isn't happy with something doesn't mean another pilot would refuse and things would be perfectly safe/legal. I am not talking about the Captain or situation in this video because I do not fly the same aircraft.
The aircraft MEL ( minimum equipment list that tells pilots, and dispatchers, if its o.k to dispatch the aircraft with this defect ) list will tell pilots if they can fly with particular systems inoperative. It might say you cannot go, or it might say you can "go" but with conditions.
Where things get "grey" is when you have multiple, unrelated systems inoperative because the MEL doesn't always look at the big picture with multiple, unrelated MELS and its ultimately up to the Captain to decide if they will accept the aircraft. This is where judgment, and common sense, comes into play.
Good judgment also applies in the air. Just because you lose a single hydraulics system ( Airbus ) for example doesn't mean return to the airport you just took off from, or "landing short" prior to your destination ( MEL doesn't apply in the air ). It depends.
I have seen Captains with poor judgment in my career.
Upgrading from FO to Captain is far more about testing their decision making/judgment than anything else assuming they have can fly well.